Go with what you are comfortable financially. I've been a hostess many, many times and have gotten many nice gifts and appreciated them all. I also appreciated it when a couple of mom's gave me a nice card with a heartfelt thank you inside.
These are some of the things I can remember:
Cards, plants, flowers, gift cards to restaurant, mani/pedi, my fav store, serving platter, photo album, candy, dinner at their house, lunch with the MTB. I'd say price ranges have been from $3.50-$50.