If I was looking sub-300, I would look for some kind of club or group that meets to build. Frankly, that doesn't seem to exist in framebuilding, while it does in stuff like aircraft and woodwork. Indeed there is probably an EAA local club, and the skills are the same.
I think you can be hard put getting the materials together for that half that price. So you are really offering a very low price, it needs to be a fellowship thing. The motorcycle frame builders are well represented in your area, I would get on ChopperHandbook site and see who you can find, lots of good welders and fabricators there. And they do reach out. Unlike bicycle guys who won't reach out unless you have insurance, the biker guys will saw an arm off. When I was in that scene guys built me a tubing bender, another guy lent me a jig, I got in business with a third guy, it's like they have a pathology and sorta think everything should be free, which is a bit weird these days.
Of course start just as you are, I'm only saying IF you strike out.