Ask for a bid broken down by room in detail ie: demo costs? 

It is "probably" not structural if it was poured after the walls with no connection to them.If it's just to make a floor, you can demo it and pour a new pad (4" thick).  

I would do all the work myself on something like this, from the demo to the replacement to the drywall patching to the tiling to the colormatched painting.

If I was trying to finish 850sqft for under 50k I'd try to find some cheap labor to do the handyman work like finishing demo, leveling floors and framing then have multiple subs bid for mechanicals (HVAC, electrical, plumbing).

The interior had been through a complete demo.

My responsibilities included demoing the existing structure and doing any environmental remediation.

I gave $6K  when demo started for HVAC installation.

Things like iron fence repair, garage demo, building a fence, replacing an exterior door, paint, flooring, etc.

The only real estate experience I have is being the demo guy for a home flipper during high school.

I think we'll be focusing on demo and fix-up in the near term, but we do need to make sure to fit time in for networking (and using this site's resources!)