I feel that with retro-gaming becoming kind of a trend and seeing the card prices going high, I can totally see how difficult it can be to collect older items. I indeed bought a Gameboy Advance SP and some games, but at a good price. Its conditions are not perfect, but it's pretty good. I bought it on ebay. Honestly, my advice is to observe the market and wait for a good offer. I simply did that. It took me a lot. Also kinda compromise on things, of course. Otherwise it's always gonna be expensive. For example my gba sp shell is kinda broken but I could replace it, so it's not that much of a problem. Same for the screen. It wouldn't take much to replace it.
Going to games, there are many fakes, so that's something to be aware of. I feel like from an online insertion it can also be pretty hard to see what's a fake and what isn't. I know that the difference is that, other than the possibility of getting scammed, is that fake cartridges can have cheaper components and therefore last less.
I read somewhere that Japanese used cartridges can be cheaper, so I'd look into that (I plan on buying some pokemon games in Japanese), but be aware of import fees.
