My understanding that this was *technically* one of the first GBA Homebrews, released by GoodDealGames at the Classic Gaming Expo 2010.
The game itself was released free online by developer DHG Games in 2007. The small studio built the GBA title from the ground up, hoping to one day see the game on store shelves. Despite months of negotiation, however, Motocross Challenge’s planned publisher backed out of the project, citing declining GBA software sales. After having invested three years into creating Motocross Challenge, DHG found itself with a finished game and no way to commercially release it.
The developer has since released the game for the iPhone. Seems there may have been a DS version in the works at one point, but from what I can tell that was cancelled.
Auction For The Homebrew Release Here
The same seller also has GBA Gorf Homebrew and Atari XE Collection Classic GBA Homebrew.