The R36s is pretty affordable if I remember correctly

Or, if you have a soldering iron and are into DIY, you can make a retro handheld console with an Arduino or a Raspberry Pi.

You can also 3D print the case and buttons (if you don't have a printer, check if your local library does).

I have an Analogue Pocket and I'd say it's better value for not that much more money; I can play all my existing GB games and more through adaptors and emulation, and that screen is amazing. Not saying it's cheap and I despise their artificial scarcity bullshit, but I don't regret buying one.