How much would I be able to sell my business for?

I started a website that is a directory for Mixed Martial Arts (MMA), Brazilian Jiu Jitsu (BJJ), Muay Thai and boxing gyms. I make my money by selling upgraded memberships to gyms that want more traffic from my site.
The cost per upgraded membership is 150 – 400 a month and I currently have 4,250 a month in revolving monthly income. My only overhead is my server and phone bill that are a combined 125 a month.
Outside of sales I only spend about 3 hours a week on site maintenance.
Every one that I have in contract is very pleased with the results and so far everyone has renewed their contracts. It isn’t the easiest sell to get new gyms, but it isn’t difficult either. If I were to put another good 5 to 6 months of sales in on the business I am sure I can get my monthly revenue up to 8,000.
Where would I start to come up with a fair price if I were to sell?

The site is mmagymsearch.com

One of the formulas I have seen is - 75% of your yearly income, minus operating expenses. And that is a rough estimate of how much its worth.

[COLOR=black][FONT=Verdana]Wow. 75% of the annual doesn't provide much motivation to sell. If that is what sites are selling for I should get into the business of buying sites not selling them. Thanks for the insight kev.[/FONT][/COLOR]

I guess it makes much sense. but i don't know for sure, cause I am not in the business.

What type of business do you want to sell tell me than i can tell you about it.

Pls. Clear first of all what u want to sell on website. What strategy have u to earn.