If you go to one of the chicken sites like Strombergs, Mypetchicken etc. they sell a variety of incubators. The cheapest are the hoverbator still air types I believe. For ease of use and reliability Brinsea have a fabulous range - from 7 eggs to 70+!
I just bought a Brinsea Eco 20 - cost around $300 but I will be hatching small amounts of rare breeds, so worth the $$.
Hope this helps a bit,
If you're fairly handy, go to you tube and search for Rush Lane. He has excellent tutorials for wiring your own incubator from an old cooler chest. We used his instructions for wiring our home made cabinet incubator. Very clear and easy to follow.