Doing the Math on a potential REO purchase. Worth it or not?

[Benjamin Fox]

REO property listed at 90k. It is a twin.

Last sold '08 for 96k 

Zestimate 140k (Id put it more in the 100-115k range ARV)

From a drive by as well as the listing pictures this is an estimate of work needed:

Roof (its a twin...1500 square foot 2 story..so not a huge roof) 

Assuming all new flooring 

Low end appliances 

Low end kitchen cabinets possibly (smaller kitchen) 

Clean up property/ Repair/repaint walls 

Extras/unforeseen due to not walking through yet 

TOTAL ~20K rehab costs (could be more or less...but for conversations sake to see what numbers work)

I am prepared to buy and hold as a rental in the $900-1100 range. OR if the numbers work possibly flip.  

Using the 70% rule I come up with offering about 30-35k for the property.  Anyone with experience..is this likely to just get shot down? Am i better off waiting for a few price reductions first and then offering.  I can promise it will not sell for 90k unless someones ready to take a huge loss.

I know to offer what makes financial sense to me and if its rejected walk away.  Because I am new to it I am looking for input on what (very rough) numbers would work for you as well as best strategy to place that offer.

I would go through with a contractor/inspector as well as re-crunch my numbers when I get more details..this is all preliminary to know how hard to pursue it.

THANKS!