The best way is by checking recent sales of comparable units. The sales have to be within 3-6 months. zillow.com redfin.com should have sales history. Have you been to either websites?
Another place maybe county register's office, which may have everything online. Simply google your county's register, or recorder.
If you want to hold and rent, then you need to find out market rent. Check craigslist.com, or local newspaper for comparable rent. I'd consider 5-10% below that to be safe.
Hope this helps. My site may have some info useful to you:
www.sunskitehomes.com