If using substrate, eco earth or peat moss is best. I would stay away from any type of mulch or wood chips to be safe.
Cresteds can be cheap or expensive depending on what kind you want. They can go anywhere from $20 up to $500+. They are one of the cheaper geckos to keep. A big bag of their food for 1 or 2 geckos will last a long time without ever having to buy live food.