We also give them both (or however many there are) the choice of doing a walk though when one moves out.

It's empty right now and I'm leaning toward replacing windows since they seem to be old as the hills (people walking by simply talking....not the usual screaming in the neighborhood) can easily be heard when inside. 

IMO.....if you kept it as a rental, your “cash invested” (your numerator) would be the cash you’d walk away with if you sold it now, after taxes.

Have them do a quick walk-thru of the properties you're considering and give you a ball park estimate. 

Here are some general details:- house is in West Hartford in a great location within walking distance of Blue Back Square- it is a duplex, but a little funky.

Purchase price: $140,000 Cash invested: $28,000 Duplex is located within walking distance of KU, main shopping venues, and a good elementary school.These 650 sq' units come with 2 bedrooms and a full bath, a stacked washer/dryer, and a big backyard.

That will refurbish provide a budget top.Ask any mobile home refurbish contractor to walk the home with you to define scope of work together and get a detailed estimate for the renovation.

Okay, maybe I was assuming a bit with the walking around inside, will email the auctioneer to verify. 

You need someone local.Even if someone like myself walked through a unit and gave you a tight number, it would be worthless because I don't know what subs/materials/etc go for in your area.

For example, say your estimated value of 140K is correct, you could possibly walk away with 50K in a cash out refinance after renovations, and 25% down payment.