Help with GBA/DS Lite Flash Cart choices

Hi all, I have been searching on this outdated topic quite a bit and haven't yet found a solid answer. My little niece has a GBA (not SP) and she will be getting a DS Lite for Christmas. My sister has spent over $2000.00 buying games for GBA that manage to get lost over time. I am more into the PS2/PSP/X360 myself so when she asked me if there was something out there that would help her save money I promised to help.

What in your opinion is the best Flash Cart for GBA and DS Lite? Something that will allow me to play dumped roms without much difficulty i.e. patching ROMs etc. Also, if you can point me to a tutorial and/or store and a little explanation on how I would be able to play these ROMs on the GBA will help me out a lot. I can find more current info on the DS Lite than on the GBA. Thank You for your help