I am building my house in one bay of a four bay pole shed currently. I had shed builders do the basic frame (including standing the poles) and heavy joists/rafters. Boring things like screwing on tin I did myself because it's pretty hard to stuff it up. The builders used the rafters roughly nailed together and into the ground to hold them straight when stood up. If doing it again I'd still get the builders in.
Once the council gave me the final sign off I did the concrete floor. I saved a fair by by doing all the boring work myself which was essentially me with a shovel and rake for about 3 days straight. I didn't have it perfectly level but I have minimum 6 inches on concrete so I am sweet. Especially as I have tractors and a truck.
It used to piss me off not being able to find out costs of these things so hopefully this will help. Rough costs off the top of my head were:
11k for a quins 9X18 four bay pole shed
8k for builders labour. I could have possibly done more but now it's done I'm glad it's finished.
10k for concrete which included 5k for the pouring, 2k for labour to help shovel it around and powerfloat, 1k for beveling the face for roller door and house part for drainage, 1k for mesh and maybe $200 for poly wrap insulation under it all. My neighbour had a compactor so I stole his for a day.
I should be able to complete my cabin for under 10k by using second hand windows and doors as well as doing everything myself. I still have three bays for workshop for my shitboxes. I spoke to the council and what I can and cannot do and they said just don't put a kitchen down and it will be considered a sleepout. I'm building to code and using proper framing timber/insulation so I'll be fine. Council have noted it on their file and that's that. I'll retire here so I don't really care about resale.
Hope that helps.