Budget wood fired oven build!!

My goal is to build a functional wood fired oven using as many re purposed materials as possible. The oven should be able to bake 24 good sized loafs as I will be baking for a farmers market twice a week. I hope to quickly outgrow this oven and that is part of the reason that I want to build it cheap. I am working my way through the bread builders book and would love to build something using Alan Scott plans but simply don't have the time or the money at the moment. Instead what I am considering doing is using the retaining wall between the upper and lower terraces of my garden to give me a good working height. Then I will pour a slab and build a brick oven on the upper terrace. I am hoping that the whole thing will be able to expand and contract a little bit to avoid cracking. The purpose of this post is to find out what experiences, good or bad people have had with similar projects. For instance I was hoping to use the abundant local limestone to build the oven but my research has indicated that this would be prone to explosion! So any advice about potential pitfalls or any awesome money saving ideas would be greatly appreciated.. I'm hoping to build something that can get me through this coming winter and then maybe in the spring build something bigger and better. I'm in Central Texas so it won't be a cold winter but there should be a good freeze or two.