Trying to add values of drop down menu options and output a total to a text field

I have two drop down menus. I want two values to be added based on what they picked and then outputted to a text field to show a grand total in a dollar amount. I am a newbie so I am having trouble. This is what I have:

[CODE]
<SCRIPT language=javascript>
var Grand_Total = 0;
function CalculateOrder(orderform)
{

if (orderform.departuredate.value >= “1” || <= “11” )
{
orderform.Grand_Total.value = 300.00;
}

if (orderform.departuredate.value >= “12” || <= “16” )
{
orderform.Grand_Total.value = 450.00;
}

if (orderform.departuredate.value >= “17” || <= “41” )
{
orderform.Grand_Total.value = 500.00;
}

if (orderform.departuredate.value >= “42” || <= “55” )
{
orderform.Grand_Total.value = 450.00;
}

if (orderform.departuredate.value >= “56” || <= “58” )
{
orderform.Grand_Total.value = 400.00;
}

if (orderform.departuredate.value >= “59” || <= “61” )
{
orderform.Grand_Total.value = 350.00;
}

if (orderform.departuredate.value >= “62” || <= “66” )
{
orderform.Grand_Total.value = 300.00;
}

if (orderform.departuredate.value >= “67” || <= “70” )
{
orderform.Grand_Total.value = 250.00;
}
Grand_Total = dollar(Grand_Total);
document.orderform.GrandTotal.value = “$” + Grand_Total;

}
</SCRIPT>

<select name=”departuredate” size=”1″ id=”departuredate” maxlength=”25″ onchange=”CalculateOrder(this)”;>
<option value=”” selected>please select</option>
<option value=”1″>May 01, 2009 — $300</option>
<option value=”2″>May 09, 2009 — $300</option>
<option value=”3″>May 10, 2009 — $300</option>
<option value=”4″>May 16, 2009 — $300</option>
<option value=”5″>May 17, 2009 — $300</option>
<option value=”6″>May 23, 2009 — $300</option>
<option value=”7″>May 24, 2009 — $300</option>
<option value=”8″>May 25, 2009 — $300</option>
<option value=”9″>May 28, 2009 — $300</option>
<option value=”10″>May 30, 2009 — $300</option>
<option value=”11″>May 31, 2009 — $300</option>
<option value=”12″>June 02, 2009 — $450</option>
<option value=”13″>June 04, 2009 — $450</option>
<option value=”14″>June 06, 2009 — $450</option>
<option value=”15″>June 07, 2009 — $450</option>
<option value=”16″>June 09, 2009 — $450</option>
<option value=”17″>June 11, 2009 — $500</option>
<option value=”18″>June 13, 2009 — $500</option>
<option value=”19″>June 14, 2009 — $500</option>
<option value=”20″>June 16, 2009 — $500</option>
<option value=”21″>June 18, 2009 — $500</option>
<option value=”22″>June 20, 2009 — $500</option>
<option value=”23″>June 21, 2009 — $500</option>
<option value=”24″>June 23, 2009 — $500</option>
<option value=”25″>June 25, 2009 — $500</option>
<option value=”26″>June 27, 2009 — $500</option>
<option value=”27″>June 28, 2009 — $500</option>
<option value=”28″>June 30, 2009 — $500</option>
<option value=”29″>July 03, 2009 — $500</option>
<option value=”30″>July 04, 2009 — $500</option>
<option value=”31″>July 05, 2009 — $500</option>
<option value=”32″>July 10, 2009 — $500</option>
<option value=”33″>July 11, 2009 — $500</option>
<option value=”34″>July 12, 2009 — $500</option>
<option value=”35″>July 17, 2009 — $500</option>
<option value=”36″>July 18, 2009 — $500</option>
<option value=”37″>July 19, 2009 — $500</option>
<option value=”38″>July 24, 2009 — $500</option>
<option value=”39″>July 25, 2009 — $500</option>
<option value=”40″>July 26, 2009 — $500</option>
<option value=”41″>July 31, 2009 — $500</option>
<option value=”42″>August 01, 2009 — $450</option>
<option value=”43″>August 02, 2009 — $450</option>
<option value=”44″>August 07, 2009 — $450</option>
<option value=”45″>August 08, 2009 — $450</option>
<option value=”46″>August 09, 2009 — $450</option>
<option value=”47″>August 14, 2009 — $450</option>
<option value=”48″>August 15, 2009 — $450</option>
<option value=”49″>August 16, 2009 — $450</option>
<option value=”50″>August 21, 2009 — $450</option>
<option value=”51″>August 22, 2009 — $450</option>
<option value=”52″>August 23, 2009 — $450</option>
<option value=”53″>August 28, 2009 — $450</option>
<option value=”54″>August 29, 2009 — $450</option>
<option value=”55″>August 30, 2009 — $450</option>
<option value=”56″>September 03, 2009 — $400</option>
<option value=”57″>September 05, 2009 — $400</option>
<option value=”58″>September 06, 2009 — $400</option>
<option value=”59″>September 10, 2009 — $350</option>
<option value=”60″>September 12, 2009 — $350</option>
<option value=”61″>September 13, 2009 — $350</option>
<option value=”62″>September 17, 2009 — $300</option>
<option value=”63″>September 20, 2009 — $300</option>
<option value=”64″>September 24, 2009 — $300</option>
<option value=”65″>September 26, 2009 — $300</option>
<option value=”66″>September 27, 2009 — $300</option>
<option value=”67″>October 01, 2009 — $250</option>
<option value=”68″>October 02, 2009 — $250</option>
<option value=”69″>October 04, 2009 — $250</option>
<option value=”70″>October 09, 2009 — $250</option>
</select></td>
[/CODE]

[CODE]
<select name=”returndate” size=”1″ class=”table” id=”returndate” maxlength=”25″ onchange=”CalculateOrder2(this)”;>
<option value=”” selected>please select</option>
<option value=”May 06, 2009″>May 06, 2009</option>
<option value=”May 09, 2009″>May 09, 2009</option>
<option value=”May 15, 2009″>May 15, 2009</option>
<option value=”May 16, 2009″>May 16, 2009</option>
<option value=”May 22, 2009″>May 22, 2009</option>
<option value=”May 23, 2009″>May 23, 2009</option>
<option value=”May 25, 2009″>May 25, 2009</option>
<option value=”May 27, 2009″>May 27, 2009</option>
<option value=”May 29, 2009″>May 29, 2009</option>
<option value=”May 30, 2009″>May 30, 2009</option>
<option value=”June 02, 2009″>June 02, 2009</option>
<option value=”June 03, 2009″>June 03, 2009</option>
<option value=”June 05, 2009″>June 05, 2009</option>
<option value=”June 06, 2009″>June 06, 2009</option>
<option value=”June 09, 2009″>June 09, 2009</option>
<option value=”June 10, 2009″>June 10, 2009</option>
<option value=”June 12, 2009″>June 12, 2009</option>
<option value=”June 13, 2009″>June 13, 2009</option>
<option value=”June 16, 2009″>June 16, 2009</option>
<option value=”June 17, 2009″>June 17, 2009</option>
<option value=”June 19, 2009″>June 19, 2009</option>
<option value=”June 20, 2009″>June 20, 2009</option>

</select>

<input type=”text” name=”GrandTotal” value=”$0″ size=”7″ id=”GrandTotal”>
[/CODE]

Note I haven’t did any type of code for the 2nd drop down menu just in case anybody says I don’t see anything. I was working on trying to get started in the right direction. Any help would greatly be appreciated.

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