One ultra cheap "puzzle toy" I like is to take an old Chipotle bag (any paper bag will do) and crumple it up with a treat inside, then hang it from a doorknob on a string. It's basically a doggie pinata. (Protip: close the door first, unless you want to listen to it getting banged back and forth a LOT.)
Some dogs will rip the "pinata" off right away, some take a while to get it down. If your dog is in the first category, you can make the toy last a little longer by complicating the puzzle factor -- put the treat inside an empty paper towel tube folded over on itself, or taped inside an empty popcorn box, or whatever else you've got handy by way of cardboard garbage.
ARCHX TDCH Pongu the Insane, CD-C, RL1X3, RL2X2, RL3X (GSD mix, b. Apr 2010)
Crookytail the Tigerwuff, RL1, NTD (Akita mix, b. Jan 2011)