Just look at the going rental rates (from the time we purchased) and subtract the amount that corresponds to the percentage ownership we hold?

I did hear of another rule that said take the ARV x 90% to take out holding costs, then subtract repair costs and the profit you want and use that as max offer price.

Take the ARV and multiple it by .7 ($227,500) then subtract the repair cost of 50k ($177,500).

Some people use the 70% rule: Take 70% of ARV, then subtract rehab costs, you should pay no more than that for the house (so if the house is worth 100K ARV, 70% of that is 70K, then subtract your rehab costs--let's say 20K, then you should offer no more than 50K for the house, leaving you with a 30K profit).

We need to subtract 6% realtor fees and our $5k material cost. 

An amount sent via email in a spreadsheet, 2 days after the date we agreed I would receive payment, was equal to 12% of the net profits...Vastly different from the 60% split I was anticipating after rehabbing, managing and selling the property...This calculation included doubled the closing costs, recouping revenue and expenses that were already subtracted from the HUD/CD.

I can't answer your first question without doing an in depth market analysis.Your second question, you take the sold comps and subtract your budget for rehab and buy, and if the result is at least equal to your desired budget, that's a profitable property. 

All these homes will sell it within a price range subtract the repair cost from the market range is what you anticipate to get.

You should have a clear means to add or subtract people.

This is the other exit for your money.4 - Take the Cost to Enter and subtract it from the Exit Comp of choice.