If you have lots of time, you might be able to build one yourself.
The thing is, it might take a lot of time/effort to get one as efficient as the one on sale for $189 http://www.sunoven.com/order.asp This one gets up to 400 degrees.
I don't know if they get any cheaper than that, as far as professionally made ones.
It's an excellent piece of "emergency" equipment, as well as a way to save money now. When Natural Gas prices triple (or more), electricity isn't going to be cheap (because that's how most electricity is generated).
You can also look in The Tightwad Gazette by Amy Dacyczyn at your local library.
Also, everything is practical and solid since their main customers are the Amish.