Lil_Kaios
If I know nothing of the game I tend to stop at 15$ max limit, though if it seems really interesting I might get it if it is more, but it has to seem really appealing to me for that to happen... Good luck on your search, I didn't realize they made Monster Rancher for the DS, I remember playing one on the PS2...
It's not very well made and for the most part it's just repetitive battling but I like it. Pretty much every Monster Rancher game in the series is better.
Although that's probably why it's not a common game.