Yes, Please post link to the schematic!! As far as cost, let's just assume a fixed cost for enclosure - say, $5. This is low, but the circuit will work even if straped to a 2x4. The transformer is a diiferent concern, especially for tube-based projects. Let me see the schematic and do a cost estimate on it. If you have time, please do the same, and we'll compare numbers. I was really hoping a tube preamp would be the first project; so, you can imagine I was excited to see your post. Preamps are pretty easy to build, and a circuit analysis should be straight forward (he says that now.)