Hello; About four years ago, in the strong part of the economic down turn, I hired a structural engineer off the books to look at a a particular house issue and give a verbal opinion. He did not have to do an official written report, just an opinion based on a look see. It took less than two hours including drive time and he agreed to take $100 cash. I basically floated the cash with no legal down side for liability with the understanding that I was not going to be able to pay him to do an inspection with a written report. He even jotted down some ideas about how to address the issue.
Unless you have difficult access like a small crawl space it may be possible to make a deal that you can afford.
Good luck