How much are you asking for? Is your forum generating revenue? If so, how much? How much is the IPB costing you a month, or per year (if per year, when do you need to pay for renewal)? When does the domain expire?
I'm asking for $100. IP.B is $25 to renew for 6 months but you don't have to renew, the perk of renewing is IPS Spam Blocker and software updates, you're still licensed to use the software without renewing and you can renew at any time. Domain expires in a few days so I thought it'd be a good time to sell.