TOPIC: User chooses fee (not pre-set)?

I'm a longtime DT Register user and fan but I am stuck on a couple of requests from a client. They want two fields:

I would like to order ___ tickets at $100 each.
I do not want tickets but I would like to donate this amount: $____

I can do the first one via a dropdown but then I'm forced to guess at the number of tickets (say, 10, and then assign the fee to each one). If someone wants 12 tickets, they'd have to fill out the form twice. It works but kind of kludgy.

I'm not sure I can do the second one at all, can I?

Is there no way to calculate based on user input? Something like:

"Whatever value user enters" times $100 = the fee charged

Thanks for any guidance.

Sorry, but there is not a method of giving a user input amount field at this time. We hope to add that type of feature, but are taking down larger tasks presently