There's a big difference between 49k miles on a liquid cooled four and an air cooled twin. 49k on a GS is overhaul time.

You can get a clean low mileage GS for $1,500 - that's a lot of scratch for an old cobbled together twin. If you really like the GS go to www.gstwin.com and lurk on the board there. Plus, they have a good classified section.