In my experience Reaper does not force you to buy.
It will ask, and trusts that its value causes enough users to buy it voluntarily (many of us here have) .. but you can keep using it for free, as far as I know.
I've never heard of anybody being cut off using it.

If concerned about it, ask them privately and explain your situation. They seem pretty reasonable to me, and would probably offer a license. Nothing to lose by talking to them.

I do not work here, but the benefits are still awesome
Make your sound your own!