Well I own a MyBB forum. Its been over 2 year old, and makes over $20,000+ a year. My first year I made $13,000+ and now I have added google Adsense, and make $500 per month from that. You make money via adsense, VIP upgrades and donations. My website is SocialEnigneered.net let me know what it could go for, thanks.
Same thing - website is not opening I went through flippa, from what I see, people just take their monthly income, multiply by 10-12 and here's the selling price. Also, you have to take into account your expenses on content, hosting, and domain name.