For me, it's a tie between a bidet and a standing mixer. Both of those were utterly life-changing for me, and with both, I regretted not getting them years earlier.
A $50 bidet is great! If you have room in the budget, though, take a look at slightly higher-end ones. Especially ones that have a built-in blow drier. It sounds silly, but it's luxurious. For something you use constantly, it might be worth an extra $100 or so.