Hmmmm.......
I am the type of gamer that has to hold it in your hands, tangible, solid, all a part of the experience. Of course I was into the TG16 when it was still on the shelf and the "battle" was between the other two guys. So that was when I attained most of my TG16 collection. Prices, for me, was comparable to the "other guy's" carts. There were those occasional sales, and I did get a few bargains at the end. Over the years adding to my stash, I have considered, $10 to $30 good prices.
What I consider one of my best moves was grabbing up a PC Engine, the original. You can get a good deal on eBay for one of these, plus get a homemade adaptor for those RCA plugs. And you can pick up a couple of games, all this, I think, for around $100, if you continue to hang around eBay. If you can find a Core Grafx II for something reasonable, that would be the best path, needs all the wires and controller in the package.
This is the easiest way to enter TG16 gaming. I think if you go head over heels at that point, you will not have any trouble saving up the cash and diving in deeper with some kind of DUO setup. I will seriously, at times, consider $40 or $50 for that hard to attain game, and finally go for it. Haven't embraced anything with that $100 plus price tag yet. (Used the word yet, which does not rule that out) But the cheapest route, my experience, for a lot of games, has been the PC Engine road. And you can always look at a game on youtube to get an idea how it plays. It can be a decision maker.
And there is just something about holding those Hucards in your hands that there are no words to express.