Their spokesperson acknowledged that all of my figures were correct and the method of valuation is correct, but they couldn't sell it for that.

In my opinion this doesn’t do compare in quality with the 3/2 homes that are selling at 150/ft

Another method, although this is more complicated (and I've only seen it with securities, so you might want to talk to an attorney) is dilution; namely if one partner puts in more money afterward in CAPEX, the other partner's ownership is reduced.

We pay 30% more today for labor than we did 5 years ago (quality labor that shows up). 

The new bid was for tear off and replacement with a quality, thick, EPDM, an insulation layer, and included four (4) sheets of sheathing (4'x8') per building.

Hard money lenders many times will let you invest in their short term debt.. ( these are commercial purpose)One thing I get a lot of is direct mail.. its exactly the same method that real estate wholesalers use.they search public records.. get lists of private owners of notes.. ( usually the target is a seller carry back) and then they blast out direct mail offering to buy the note from the current note holder.. the pitch in 99% of those is all the same  same buzz words..

My preferred method to learn now is podcast.

I'm starting to look into CFDs and am wanting to get a little more precise than the "stairstep" method of bidding.

Which method will grow our investment without jeopardizing our plans, or become a roadblock in the future?

It's a proven method.