Unfortunately you’ve just hit upon one of the biggest arguments used against Reaper — it has a pretty limited set of good effects and only a couple “instruments” like a very barebones synth that I would never use.
But that’s not why Reaper users love Reaper. It’s in its performance, flexibility, customization, etc. In another league as far as these things go. But you get almost nothing for free as far as instruments.
I’m fine with this and wished it weren’t a deterrent for folks like it often is. The best effects and instruments are not baked into any DAW, they’re the ones you have as VSTs that are portable to whatever DAW you want.
Reaper is a fraction of the cost of Ableton. The only other “tier” is that for just $60 they’ll sell you Reaper with a personal use license only. No limitations or changes in the software itself.
Reaper has a plethora of built-in effects and you can script your own in JS or Python or EEL2. You'd have to use third-party synthesizers though.
That said, the GUIs of said effects are basic, but I personally still find them useful.
There is no difference between the evaluation, non-commercial and commercial tiers.
I'd say, give it a try, the days when Reaper was a niche DAW are way in the past. Especially if you like the idea of being able to customize every corner of your DAW, Reaper is the no-brainer choice.
Nitpick: the JSFX audio effects you're referring to are scripted in EEL2. Reaper itself can be scripted with Python, Lua and EEL2 (see http://reaper.fm/sdk/reascript/reascript.php). It also has a C plugin API.
RE: Ableton -- does Reaper have anything like the clips-triggering interface that people interested in DAW-as-loop-instrument often use Ableton Live for?
Is there a single version or different tiers like abelton, where you get almost no instruments with the cheapest tiers?