What's A Good GBA Flash Cart?

I have a DSFire, which unfortunately shit the bed about a year ago, since there haven't been any firmware updates. I just ordered an R4DS SDHC, which should solve that problem, but I've been doing some research on NDS-compatible GBA FlashCarts. I can't seem to find the "one" that everyone uses. An equivalent to the R4, if you will. Does anyone have a good brand?

I've never had one myself, and from what I understand they're sort of scarce nowadays. I recommend you visit this little section of a site here. They'll know what you want, there's also this topic that's sort of relevant to your interests. I hope you find a good one!

I ended up settling for a mini-SD card compatible SuperCard Slot-2 device. One thing I don't understand though, is why GBA carts are more expensive than DS ones? I bought an R4 for $6, but the GBA one cost $13.

If I remember correctly, GBA carts have RAM, while DS flashcarts do not have/need any, due to the system already having it.

That could be it. I know that the description said that it could be used as a DS expansion cart as well.