Might be worth getting a PO-12 or PO-32 Pocket Operator (the drum machine models). Beyond one of those and the PO-33 I wouldn't go too deep into that range as they're way more toys than full fledged synths but that could be all you want (it was all I wanted tbh) and they're a lot of fun and will retain their value if bought used.

I keep a PO-32 beside my desk to mess with when I get frustrated coding.