Why are the GBA eshop prices different?

I've noticed that some eshop GBA games are $6.99 while others are $7.99. What makes one cost more if they are all GBA games? Popularity maybe?

Good question... Don't think Nintendo has said why. My guess would be popularity / length of the game.

the do that with gameboy games on 3ds also...some are 2.99 others are 3.99

I see. Rarity may have something to do with it as well. I find this a bit odd. They should settle on one price for each genre with the exception of indie games.

Probably because the games that are more expensive are most likely better, or the cheaper games have been on the eShop so long they decided to reduce the price?