the 38mm biogon is a much more highly corrected lens. The 40mm is a retrofocus design, so it has distortion in it. Not that it is bad, by any means, but the Biogon is the superior lens.
There are the three varieties of this camera - the early chrome lens (uncoated, b50 filter size), the late (black) chrome lens (ie still a C style lens, but in the black body, most likely with T* multicoatings, b50 filter size), and the CF style lens with the b60 filter size, rubber focusing ring, etc. They were named, in order, the Superwide, the SWC and the SWC/M. The current model I believe is still called the 903 SWC.
For a fair valuation example, I'd use the KEH website - they sell their gear at very fair prices, and usually the actual condition is far better than the grade would suggest. Their idea of Bargain is usually most people's idea of Excellent+ . For example, they have a chrome lens Superwide in Bargain condition for $1479. A 903 SWC in EX+ is $3799. A SWC/M should fall somewhere in between those prices - my guess would be $2000-2500 depending on age, condition, etc. You can tell the age of the camera from the serial # - the first two letters give the year in which it was made. Use VHPICTURES to obtain the age (V=1, H=2 etc).