"Even" DS Games is not really applicable anymore really.
Games for consoles tend to follow the same cycle every time. They get cheaper as the current console gets older, then once the new Gen starts, they get really cheap and once you're about one to two generations removed, they get more expensive again.
It has been the DS's time to get more expensive for a while.
PSP has also started to get more expensive, though not remotely as much as DS games, since the DS was more popular.
Games for consoles tend to follow the same cycle every time. They get cheaper as the current console gets older, then once the new Gen starts, they get really cheap and once you're about one to two generations removed, they get more expensive again.
It has been the DS's time to get more expensive for a while. PSP has also started to get more expensive, though not remotely as much as DS games, since the DS was more popular.