and call the owners and ask what their property is renting for and how recent the last rent increase etc.
Would your MLS like to purchase my MLS's? One of mine actually prohibits listings of rental property. The other two just don't bother with it. I have had to slowly build up a database.My MLS has a specific search function (surprisingly under "Search") for several types, including but not limited to:
SFR, Condo, Townhouse, etc
And in each criteria, one can specify GLA, yr blt, price range, etc
If your MLS does NOT offer said ... then I'd be contacting local brokers, property management companies, etc to get their take/info