I'm new to Reaper but bought the Non-commercial licnese for personal use. My impression with Reaper all along is this was mostly an honor system price scheme. The demo is fully functional without limits. They say try it for 30 days then you "should" buy a license, not that the demo will cease to work. For $50 compared to other programs I thought that was cheap money so after a quick look around I just paid up front. The download is the same regardless (my experience anyway).
The Commercial vs non-commercial to me appears also to be an honor system and a very smart way for Reaper to get their software into the hands of alot of younger artists/engineers that may not be able to step up to the full fee. But the program you use is the same regardless of whether you paid $299, $50, or just keep using the free demo.
My view on this? $50 is a real low cost way to get your feet wet even if your selling your music. If you are doing really well selling it, you should give Reaper their due and upgrade. If not, I'm sure they aren't worried about your small number of sales with their low cost software. If you use Reaper to charge others to record, you basically are in business. At some point you ethically should pay Reaper for the upgrade. My only caveat is that if you record others as a exceptions even if you get paid, would be nice if you had the commercial version but I doubt again, that Reaper will sweat it.
They want the $300 bucks from those that will use it make well over $300 using their software, but want the smaller guys to use a fully functional software package of theirs versus some other demo. Even if they only get $50.
So if you make mp3 with the demo or $50 version of Reaper and sell a few dozen copies, don't loose sleep. If you start making huge amounts of money (enough where you CAN afford a $300 DAW), you should do whats right and step up and pay Reaper at that point. If you don't no one will be the wiser but to me like some struggling young writer pirating a copy of MS Word, writing a novel, it becomes a best seller, then they continue to use the Pirated copy of Word to keep writing when they should just be legit and buy MS Office.
Sorry to go on.