http: //www.collectorssource.com/index.html
These guys got dewat / deactivated beltfed guns. No mg08, but they got some other old goodies. Never dealt with them, but maybe they can give you a good estimate on your item? Vickers for $3500, maxim $1900, mg42 $5000. Prices vary, no pattern i can see (age, origin, appearance, quality, etc?) but they're all pretty expensive!
edit: Offtopic, but could somebody pm me regarding the mg42 deactivated value. I am interested, but i want to know if that is a good price?
edit 2nd time: was thinking mg08/15, or whatever the german one is with that funny hump on it is.
The maxim for $1900 similar to yours?