How to compare old road bikes I'm looking for a retro road bike and found a Gudereit T30 with a steel frame, 12 gears, and Mavic rims.

How can I compare this bike to more common bikes to figure out its value?

Comparing the shifters and gears seems easy (DuraAce-Ultegra-105), but how do I compare the steel frame and wheels?

Some pictures:

http://cl.ly/image/1g1h2G0c2d2O

http://cl.ly/image/2b2m2G2l0J0w
A reasonable estimate can be found using a site like Bicycle Blue Book. This site is a database of used bike sale transactions going back for almost a decade, and has a number of pretty obscure manufacturers listed. You can even add upgrades you have made from the stock and get an estimate of how that changes the value, though it doesn't account for things like racks, fenders and lighting systems you would add to a bike to make it a competent commuter bike.

I've sold 4 bikes within the last 6 months, and all 4 sold within a reasonable range of what was listed on that site.