@Chris H. a quick method to evaluate what the price should be is to take the net operating income (NOI) divided by cap rate (CR) equals value (V).
For NOI, take the monthly rent and multiply by 12 (months) then subtract 50% (conservative rule of thumb). Cap rate is location based so you'd have to determine that based on recent sales in your area (i.e. comps). Then divide NOI by CR.
For example, let's take a MF with 2 units, each with $1,000 in rent per month in a 10 cap location (tough to come by these days in a sellers market but makes an easy example).
Monthly income = $2,000
Yearly income = $2,000 x 12 = $24,000
NOI = $12,000
Cap Rate = 10%
Value = $12,000/10% = $120,000
As I said, in a sellers markets it's tough to find deals where you can offer a price that is justified solely by the numbers, conservative numbers at that. But this should give you a basic idea of where a price should be.
Don't forget that MF's are supposed to be priced by the numbers! So always consider that before your offer.
Good luck!