I can tell you that I have not had luck with appraisals in the CLV area, not sure if that is the market you are attacking. 

Market rents are above $2k, per door.

I found this deal off market and found agreeable terms with the seller involving a midterm lease during renovation.

Private money How did you add value to the deal?

My concern here is that depending on where your property is located, that might not be the market standard in that neighborhood.

Hopefully along the way your properties appreciate, you pay down debts  (mortgages) from operating income, and you get market appreciation on what you can rent each unit for - giving you more income each month. 

Maybe % of purchase price (though that would mean low estimates for killer deals, and higher estimates for hot market properties)?

While the market is stalling a little my wife and I are considering the "Shred Method" to pay off some of these properties faster.

What type of traveler are you marketing to?

They may come up but understand that rental rates are generally well below market (hence the discount) and these deals are largely off-market if you're able to find them.