If you are really out of money and have strong will, start studying electronics (get some books from your local library), learn to solder, and then look into the net for schematics. I don’t think you’ll be able to build compressors at first, but you can build high-end preamps with a few bucks, especially valve preamps… those are very easy to build. In my country it’s very hard to find line level transformers, but I’m sure it will be extremely easy to get them if you are in the USA (Jensen transformers), Canada, or any big country. Anyway, I know you’re not looking for preamps, but practice will improve your skills quickly, and then you’ll be able to build more complex stuff.