My property manager sent a request to their contractor to make the unit ready and came back with a $5700 estimate which is blowing my mind.

In my experience, HUD (property management company working for them) is very reasonable and willing to accommodate most of your reasonable requests.

is there a need to request a retroactive permit ?

I'd like to get a better idea before I call and stumble over my words try to explain my request. :)

I suppose while you are making the payoff request, you can ask if the Mortgagee would consider an assumption.  

Can I request and extension or delay acceptance until the place is dewinterized?

The cost would be $10 per appraisal, you set the limit on how many you want, say 5Users see your request, and submit their appraisal which would include:Price (range)Comps to justify the price100+ word description justifying the appraisalMarket trending UP or DOWNEtc undecidedOther Considerations:The requestor can like, or rank the valuations out of 5 stars.For quality control, users begin earning a % of the appraisal cost ($5-$8), once they submit 10 "quality" appraisals. (10 appraisals with Likes, or 3+ stars)------Background.I analyze 60+ properties per month for my own business needs. 

The only one I've put earnest money on was when the seller was an attorney, and he requested I put $50 down on it.

Corrections in the below comments are requested. 

I'll send you a colleague request and we can chat more about it