I Have a 3BR 2ba 1500 square feet house under contract for $59,900 and a estimate repair cost between $20000-$25000.

So far her has received 2 estimates. $800(IMO too low) and $6100(IMO way too high).

Besides calling a general inspector to check for obvious issues, and a general contractor for estimating rehab costs, is there anything else I can do to reduce exposure?

The Book on Flipping Houses and The Book on Estimating Rehab Costs.

I estimated 22K for all of the repairs and upgrades using the high estimates provided by Homewyse Here are the numbers: Taxes $3,000Insurance $1,500 estimatedVacancy $1,400 one monthLawn care $600Misc  $1,000Comp rents for he area are about $1,495 but I am estimating $1,400 to be safe.What do you think?

She says he's one of the only reputable and affordable contractors she can find due to other contractors' lack of follow through, availability to do estimates and lack of quality work in the past.

I did already get one estimate for $6300.

@Adrian WatkinsI have also heard that Tucson is a good Buy and Hold city but I struggle to find properties that meet the minimum 1% rule (Estimated Rent/Purchase Price).  

The bedroom ceiling drywall, one wall, and the bedroom carpet all had to be replaced.To be fair, the tenant had no access to the downstairs bedroom, but his negligence to let me know of the water leak in the upstairs kitchen led to extensive water damage.The insurance company said they estimated the damage to be $5,489.

I estimate that we've spent a few thousand in medical bills as a result.When we asked Fujitsu about the mold issue, the said that we should hire a contractor to come clean the units regularly.