Do you have any local garden centers? Smaller, family-owned stores usually have the clay or plastic saucers that are deep. You can even ask them if they have used ones, which they will generally sell for less.

For babies I use 4" saucers, then they go up to 6" if they are 500g or so and need one(don't have any that need a hide at this size). My Walmart has them for 50 cents apiece for the 4" plastic saucers. You may also try Home Depot or Lowe's, and possibly Ace Hardware if you have one.

Plastic cereal bowls from the dollar store also work great.