Here's some info and price range for an appraisal.

Depending on the type of appraisal and type of report your lender wants, they may require a "complete" (2-3 approaches) or "limited" appraisal (1 approach) and a "self-contained" (very detailed) or "summary" (less detail) report. For apartments greater than 4 units, a general certified appraiser will typically be required and would be considered a commercial appraisal. Fees can range from $1,500 to $5,000.