Is there a field form rule for State?

What do you mean by "this x amount"? Are they charged a different cost, do they get a different score?

If it's the former, you can use visibility rules. If it's the latter, you can create a flow that changes the lead score by X amount if they fill out the form and they're state is one of the five.

Hi Ashley!

Thanks for the reply! The five state will receive the product and the other states is not eligible to receive the product. 

Thanks for additional information!

@Marvel M Not really clear what you mean by "[form field] rule." Are you trying to create a dropdown of 50 (+ territories) states and passing the chosen state to the back end for flow processing as @Ashley Deas notes?  Or are you talking about doing some sort of browser-side form validation before allowing the data to post back to Marketo (i.e only allowing users in your five states to even submit the form)?