I found on ebay a brand (I can't remember which!!!) that sells 4 puzzles in a box, a 4p, 6p, 8p and 12p. when dd was about your boys age I gave them to her with photocopies of the puzzles and she would solve the puzzle by using the photocopy. She got the hang of how to put them together that way too. Also wooden puzzles that make shapes are a good idea.
I wouldn't worry about pre k at all. If you need daycare, try an in home provider that can tailor fun activities for your child. If that's not an option go play based.
