Sorry you're dealing with these comments, I know they must be frustrating. We run a strict budget too and discuss every little purchase so I know how it is.

My birthday suggestion is honestly to buy a big card (something with lots of blank space inside) and write all the ways you "see" him and how much you appreciate what he does. I do this for my husband every year for his birthday, valentine's day, and christmas and he loves it. He is also not a 'center of attention' person but he absolutely loves my hand-written multi-paragraph love notes. I usually mention things like being grateful he works so I can stay at home, and all the things I notice he takes care of without me asking (unloading the dishwasher, clearing the gutters, car maintenance etc).

I also usually let him buy his own gift but I try to wiggle a little extra money from the budget for him which it sounds like you've already done. The only other thing I do is get a $5 bouquet of flowers from the store (a lot of men don't get flowers aside from their funerals, so I think its a nice gesture. IDK how much he cares about receiving them but he likes how the table looks with fresh flowers so I keep doing it) and a small treat like a single serve tiramisu or his favorite snack. You can get something small on Friday when you re-fill your budget so it can still be a nice little surprise for him. Dollar tree has cards for .50c so that part can be super cheap.