Have you looked here
? They have a toddlers and preschoolers section (ages 2-4). And it's free, so anyone can afford it
It's one of my favorite sites.
I have quite a few other preschool sites (all free) listed here
ETA: Just an idea, It's quite easy to do your own unit study, esp for preschool, there are tons of free worksheet printables easily searched for or, if you're good in word, make your own worksheets.