Let's assume the 1-year government bond yield is at 5% (it's not, but it simplifies the math, so bear with me). As a gross oversimplification, that means that a $20 investment today will produce a risk-free return of 5% ($1) at the end of a year. The converse is also true: if a risk-free investment produces $1 in revenues over the course of a year, then the investment should be valued at $20.
Value = (Annual revenue) / (interest rate - growth rate)
The interest rate here is the interest rate that takes into account how risky your business is--the rate you'd be able to borrow at, the "cost of capital". Let's say you could get a loan (secured only by the assets of the business) at 15% interest, and that you expect to grow by 5% per year. Then per $1 of annual revenue:
Value = $1 / (.15 - .05) = $1 / (.1) = $10
Let's assume the 1-year government bond yield is at 5% (it's not, but it simplifies the math, so bear with me). As a gross oversimplification, that means that a $20 investment today will produce a risk-free return of 5% ($1) at the end of a year. The converse is also true: if a risk-free investment produces $1 in revenues over the course of a year, then the investment should be valued at $20.
So, if your website was risk-free, it'd be valued at ~20x your yearly earnings (after-tax net profit).
Of course, it's not risk-free, so that will discount the price.
On the flip-side, it has potential for growth, so that will increase the price.
For comparison, other tech companies trade at:
Microsoft: 23x earnings
Yahoo: 46x earnings
Apple: 47x earnings
Google: 53x earnings
Salesforce: 688x earnings
Facebook: 500-1000x earnings (http://blogs.reuters.com/mediafile/2007/10/25/keep-an-eye-on...)
1000x earnings is what Yahoo was valued at in 2000. That's probably a max on what you can ask for :). Given your growth potential, I'd say 20x earnings is probably a min.
Good luck!