You may want to just go ahead and factor another $20 for new wheelsets with gears. I would agree that you should be able to find one of these for $50 or less. In fact I may have one I can sell.
Besides that, depending on your CGW goals, the S2 is not really a locomotive to get too worked up over. If you look through the color guide, you will notice that all the S2 (#'s 8-10) pictures are out of Chicago (the GeePs are this way too) and the rest of the S fleet was in southern Minnesota.
If you can get one at a good price, definitely go for it.
Jason