First, how much work will the new owner need to put into it? $15,000 worth of work per year? Remember $10k only pays for about 5-6 hours of work per week.
Second, how likely is it that someone can de-seat your site? That makes it much less likely that the site is worth so much.
Third, would a competitor, given a decade, be able to build what you have built with relative ease? This is key to how long you would run a regression.
So, if you assume that the site is good for 12 years, a simple regression would give you about $200k as a valuation. BUT, that assumes they won't need more than 5 or 6 hours a week of work on the site. AND it assumes that it can't be easily built by a competitor. AND it assumes your site will stay that profitable (which is usually true in something like real estate, but not in technology which is constantly changing).
Even if you think the site will stay relative for the next 25 years, it's value wouldn't top $300k simply because future dollars aren't worth as much as present dollars in a net present value calculation since there is an opportunity cost to tieing up your money.
However, your site may be growing. In that case, it might be worth more.
So, if your site needs a full-time programmer, it's worthless. I mean, it's worth something to you because it can be your income. However, it's not worth anything to an owner since they'd be paying all of the income to a programmer (yes, even if that's themselves since they aren't getting the site for free).
So, it's really dependent on how much work goes into keeping it alive/competitive. This might be your job/income. That's good for you, but worthless to an owner purchasing it. If it requires about an hour of work a week to keep it competitive and it will be that way for a decade, it's probably worth north of $200k.