That was just a simple rule of three I conjured based on the value of Bermuda(dot)com vs China(dot)com.
Most appraisal tools make an average around key word quality, history of sales with those, traffic rankings and age. With that said, I don't think many of those tools are very reliable on their own. For example, I think the GoDaddy tool usually has ridiculously high appraisals, so I rarely use it.
Then there's the other element that goes with your own marketing. Maybe there's a company in Bermuda willing to give you 10K up front. Many times its all about finding the right place and the right people.