Best place is to look at the for sale threads of similar machines on the forum. I've seen similar go for between £1500-£3500 in the last year. Yours looks to be very well presented which will help, but I think it's ultimately down to your patience and finding the right buyer.

Slightly depressing when you consider how much the components cost and how much time and effort you've put in - but perhaps this is just the wrong audience to be selling to in that most people here want to build their own. You also need a buyer who can appreciate the quality and not be put off by the handmade nature, tough market!