Do a search for "cob earth oven" or on Instructables, or check out your library. The first oven my friend built in his parents back yard cost less than $100, used the clay from his parents back yard (mixed with sand) salvaged wood supports, and he used normal red clay bricks instead of firebricks, it worked just exceptionally well for bread and pizza.

So I'd say don't let anyone fool you by saying that you need a $3000 pizza oven. Humans have been cooking with wood and bricks for a long time. Go to town on it if you have the space in your backyard, and reuse as many salvaged/ local materials as you can.