I got the combo pack, hygrometer and thermometer, for $11.99. They are on sale now for $8.39 for the set. Or, you can just get the hygrometer for $5.99 regular price and it's on sale now for $4.19.
http://www.petco.com/shop/en/petcostore/product/imagitarium-thermometer-humidity-gauge-combo-pack
I insisted on asking a lot of questions about the reliability, and the manager came out and told me he uses them for his reptiles and that they work very well. I have used them for all my hatches, and it's been helpful. I like having a second thermometer. That way, if I move some chicks to the brooder, I can put one there.