If your main concern about DIY keyboards is experience, most DIY split keyboards only require through-hole soldering, which is easily doable even with a cheap soldering iron.

The Sofle keyboard is a popular split keyboard. https://github.com/josefadamcik/SofleKeyboard I haven't checked, but I'd believe it's possible close to that budget. e.g. Keyhive have a DIY kit https://keyhive.xyz/shop/sofle