How to Analyze a 5-unit multifamily with no cap rate data

[Raj S.]

I'm new to multifamily investing (have 5 single family rentals) looking at a 5-unit property. Property is poorly maintained, lacks proper paperwork on expenses, but is in a great neighborhood and presents a great value-add opportunity at the right price. What I'm trying to assess when pricing an offer is, how can I get enough recent commercial rent and sales data to determine a likely cap rate for an eventual refi or sale in underwriting. In residential, comps are available on Redfin or Zillow, but I just don't know how to price this offer appropriately.

Any advice for this newbie?