Better to have someone working on them than having them sit.That being said, I don't take multiple estimates for every job.  

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookDownload BP’s newest book here some good due diligence in Chapter 10.

I doubled this estimate for my calculations.  

From what I see on BP there aren't a ton of areas where my numbers are even feasible.Another equation I do for testing a property is rent - 30% (vac&main) - PITI (15 year note) = reasonable estimate of long term cash flow. 

Im not sure If it will get that high in 2 years but 340-350 is a reasonable estimate.  

If the repair costs is estimated by HUD then you probably should consider having someone else do the estimate.  

The flat rate charges I've seen so far seem to push my estimated monthly PM expense up to 13 - 15% of monthly income.  

As a rule of thumb, a 50% expense ratio is conservative and a good estimate.  

Try to estimate with a spreadsheet while walking through all the repairs that will be needed. 

I am estimating we can purchase this home for 35k to 45k it would need 40k to 50k in repairs and the ARV would be 175k.