Don't buy OG unless you have the ability to connect it your TV and you're willing to hunt down games on eBay.
I def recommend the SNES Mini or even the Switch Online library as a start.
Super NT is the next viable option if you do decide to go full cartridge route but very hard to get and expensive.
There are cheap SNES-like consoles but they're of middling quality.
Ebay is literally a last resort for buying retro games, IMO. It's where you'll see the absolute most inflated prices. If you are going to jump into collecting, here's a few things to keep in mind:
1. You are going to have to hunt and you're going to do it in a bubble market as someone had mentioned earlier. Prices are going insane right now and have been for almost a year.
2. Get to know your local retro game shops. Preferably not franchise/chain stores though they can also provide good deals. Those smaller shops generally have to compete for business and usually undercut the competition on price AND you can haggle with them to get a better deal on a game (within reason).
3. Facebook marketplace, Craigslist, etc. are actually pretty great if you have patience. I bought a nearly mint copy of The Adventures of Batman and Robin on the Sega Genesis from a Facebook marketplace seller a few weeks ago for $40. It's a game that sells for close to if not well over $100 on Ebay.
4. If you have a local collectors group in your area, join it! These folks are not only your competition but they can be very good friends keeping an eye out for games on your want list if you do the same for them. I've gotten texts from local members of a collecting group I'm a part of with pretty good deals just by reciprocating.
5. It's still going to be expensive as hell. The Batman example above is an exception. I recently bought a loose copy of Demon's Crest on the SNES for $120. That has now shot upwards of $170 in the span of a few months.