Booking form linked to prices

I am designing a form for my project where i need to make a booking form for a campsite website where people can add their details and their preference of stay eg. static caravan, tent, …. i have done the details bit but i need to do some sort of drop down menu linked to how much the static caravan costs and tent etc giving me a calculated final price. Does anyone know how i would go about this?

Deri Reed

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