It seemed like a great idea! GBA shell, battery, display swap 

Brother, that kit on Ali Express is actually a great deal considering what you get. Buying that stuff piecemeal from places like Retro Game Repair Shop or Hand Held Legend will easily run you over $100 just for the parts. You also got that GBA in excellent condition for a great price. I don't think I've ever seen a listing for similarly modded GBAs for less than $200. Many sell for closer to $250, in fact. If you were all-in on this for around $115 then you actually did great, AND you got to dip your toes in rebuilding a GBA which is even better.

gameboy mod with classic music in front of sunny window so chill

You make it sound harder than it is.