I did one a few years ago. the total kit was around $200. this included the screen, some solder kit to modify brightness, and a new front screen glass.

I also took the opportunity to upgrade the case and li-ion battery.

all for a Christmas present for my kids that they never play...

There’ve been tens of mods over the years for backlighting a GBA v1. Nowadays there’s clone hardware that plays anything via emulator.