Setting the sale price of the asset or business that you have built is incredibly hard - how to put a $ value around all of your effort, the time you have spent and the stress you have experienced building something from the ground up?
Typically you should use the average monthly profit of your asset or business to establish an asking price or sale value. Profit is what buyers look for when looking to purchase an asset or business as it relates the purchase amount to the amount of profit the new owner will receive once they start running the business. Potential buyers can then forecast if the business continues at its current performance when they can expect to cover their purchase cost and make actual profit.
Generally a realistic sale value is between 1-3x the annual profit of an asset or business. The higher (larger) the multiplier (i.e. 3x Annual profit or higher) the longer it takes for a buyer to break-even from the cost of the business and so only the highest performing and most attractive assets or businesses reach larger annual profit multiples.
As you can see from the above, an estimated sale value is a range from low to high. An asset or business can sell anywhere within that range - and possibly higher if there are people looking to buy exactly that sort of business. As a guide, you would use the higher end of the range if the profitability is trending upwards over the past 3-12 months and specifically over the most recent 3 months; and the lower end of the range if it is static or even declining. This is because upwardly trending businesses and assets represent stronger investments for people as they are performing better.
This is a guide only, there are a lot of market and economic factors that affect sale values for businesses. Generally setting a sale value or reserve around 1.5 - 2x annual profit is realistic, will generate interest and not be considered 'over-priced'.
If there is very little (or no profit) profit, then a sale value can be based on visitors, traffic or downloads. By looking at the amount of interest in the business (visitors etc) and where this interest comes from (website visits from people in USA for example) a value can be generated based on what sort of revenue could be generated from advertising. Advertisers commonly pay per impression or per click and the actual amount varies by country.
Please note that assets or businesses without profit are harder to estimate for sale as most buyers are looking for businesses that have a profit.