You should charge the market rent in the area you are in based on what you are offering.

I have also always gotten an assist from market appreciation but let’s ignore this.  

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.

I can find lots of options through online sources (Zillow, Redfin, Rentometer, etc.), but since none of these sites available to me show leased properties I'm having trouble finding good comps to list on the appraisal dispute form.

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. 

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

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

But I know that I've never seen a property sell at auction in our market that was any where near enough of a deal to really whole saleAlso- you're buying the house outright with cash, IF you found a killer deal then I think you'd actually have to close then re-sell to an investor.

@Gina Rocillo look first online so that you don't alert them to any issues.Good Investing...

I know the market fluctuates and that can be a factor, but generally speaking.