Calculate

Using drop down or radio options, how do I get a calculation of price. For example:

Quantity 25 = $40
            45 = $60
            65 = $70 

I want the form submission to look like this, below... but the only way to do that is get the price and quantity in separate fields. How do I do this without causing confusion? The purpose of this form is to generate a quote. 

We've received your request for {quantity} of items. The estimated price is {price}. We will contact you within 24 hours to finalize your order.


Today's Date {todaysDate} 
Date Required {dateRequired} 
Customer Name {customerName} 
Phone Number {phoneNumber3} 
E-mail {email4} 
Address {address5} 

Quantity {quantity} Estimated {Price}