I'm not really into the handheld or console market, so I cannot give you any ideas there. Games-wise for pc, cheaply, there's:
Age Of Empires 2 HD! Coming out shortly. AOE2 was really great. Pricerange 10-15 Euro, so probably 15 USD.
Antichamber! If you haven't already picked it up, it's a super fun puzzler, and goes for 19 Euros.
Zeno Clash 2 is coming out the 30th of April! ZC 1 was gorgeous, interesting and fun, and this one is supposed to have an even better engine! Going to ship at 14 euros, so I'd save up 20 USD if you want to wait for reviews.
Baldurs Gate EE added some pretty cool characters, and some new areas, so if it's been a while since you played that, I'd pick it up (from Beamdog, there was some issues with the Steam version) for the 20USD it's at.
If you don't already have it - I just replayed Fallout 2 with the restoration project mod. That added a lot of interesting quests and places. If you have the game, you can play with the mod for free! If not, it's just 10 USD on gog!
To the moon (available on GOG), is just 10 USD, and is a fucking gorgeous interactive story experience.
On the 3DS; if you are mainly going to be using it for retro gaming, I'd get an emulator for your smartphone instead (if you have one), since that'd save you a bunch of money. If you can survive a bit worse controls.