how to value a property WITHOUT a formal appraisal

I own several 4-plexes in the Jacksonville FL market. I'd like to get an idea of their market value (just for my own satisfaction), without paying the $X00 per building for a formal appraisal - again, the valuation is just for my own personal knowledge, not for any financing, sale, etc. 

I've called several places looking for a quick BPO or desktop appraisal, but all the places I called say they don't do this for multi-family. Does anyone have any resources they can recommend for this?