N/A Best springer to learn on

TX200 is hands down the most easiest spring gun to take down.

I’d start with a Crosman or Gamo product to start on. Hate to tear into a 500$ plus rifle and have it go sideways. Plus the more inexpensive rifles have a lot to improve on. If you can find a Hatsan with a Quattro trigger that would be another good one. Triggers are fairly complicated though. But good to learn on.

Need to decide on your definition of cheap. TX200 is an excellent gun. There was a used one in Classifieds a week or two ago, I think it was 6 bills? Probably not the gun to learn on, and sliding breech setup adds some moving parts over break barrel. Might look for a Weihrauch HW30S used since you plan to take apart anyway. Believe they’re under $400 new, not sure what used prices are. Not a lot of pre-load so not hard to disassemble. And several folks here who could walk you through. Beyond that, Hobbyman has the right idea.