need some help

I’ve seen sites that update select choices to previous select choices made, for example: ebaymotors.com when you select a car make it will update the options for models.

My site is going to have an input called sizes, where the user can type different sizes, example: small,medium,large.

I would like the form to autoupdate so when they hit a button or something a new thing will be added to the form for each size they just typed, example:
Price of size small: <input type=”text” name=”price0″>
Price of size medium: <input type=”text” name=”price1″>
Price of size large: <input type=”text” name=”price2″>

and if their sizes were: pt,qt

the form would update with:
Price of size pt: <input type=”text” name=”price0″>
Price of size qt: <input type=”text” name=”price1″>

any ideas?

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