First thing you'll need to do is get the model - One way is to get the serial number off the body and look it up or have someone look it up for you:
http://www.rolleirepairs.com/models.htm is a place to look for older Rolleiflex's. Make sure you do a sanity check and verify the lens matches the one that serial number is indicates...
Prices are all over the place - in good condition, I've seen them go anywhere from a $200 to $6000 or $10,000....
It looks to me like I have a Rolleiflex 2.8C Xenotar from sometime after 1953, but I can't find the serial number. I see serial numbers on the lenses, but where is the serial # for the body?
Anyone know what this might be worth? Works fine. Looks very clean internally and the lenses are fine, but the outside is a bit dirty and worn, but no dents. Shutter seems to work fine.