You should try Puzzle Quest for DS, a used DS and cart should not be that bad, plus you can sell it all if you get bored later for not much loss and you won't have that feeling of guilt as you spend money. The game is great for short trips, basically just close the DS and it sleeps until the next time you open it, then almost instantly you are right back where you were. Charge the DS when you get home, and you might not even ever have to power it off.