I don't know if there are places willing to let you work in exchange for a bus or whatever. But I read your post and sort of can identify and so, wanted to chime in with a little encouragement maybe.
I've been also looking for a bus to convert. I've looked EVERYWHERE! ...ebay, Craiglist, asked around and even run ads in the local Trader's Post and Penny Trader. Here's the important thing. I have viewed literally dozens of YouTube videos of folks doing their own conversions. They all have similar stories and invariably they end up getting a good bus candidate for a really low price! But in every case, it took them a considerable amount of searching and it took time. They were patient.
I also have been patient. I've had my heart set on a Blue Bird All American RE (rear engine) with some basement storage. I used to be a school bus driver and this is what I drove. I knew that it was a really good bus adn I knew I would love it. But I've also tried to keep an open mind. Out of the clear blue, I found the bus I just bought this week and it blows the BlueBird away.
I bought a 1998 Prevost H3-45 with 164,000 miles on it for $6000. I realized that, if I had gotten impatient and made too early of a jump, I would never have found this bus. So please take heart and hunker down for a long search. There are deals out there and good buses all over. You just need to connect the dots so to speak.
My Prevost's name is "Miss Gloria."