If you're looking for a capable budget 9mm with lots of options, don't overlook the PSA dagger. It's almost half the price of the Glock 19 G3 it's cloned from, and it accepts the majority of the same parts. Same mag as the Glock 19. The trigger is about the only part of the gun that gets any criticism. Many other parts are often considered better than the Glock. It comes in about 30 different models and configurations, including all kinds of options for threaded barrel, optics, lightweight receiver, etc. Check out the reviews for it. You can order just the receiver, lower, or any individual parts to build your own. Fun cheap 9mm project platform.
https://palmettostatearmory.com/psa-dagger.html