Look at Flippa for benchmarks, and contact FEI International for an appraisal.

Most people will evaluate the company based on its revenue and margins. If you think the assets have potential value outside this, e.g. for another type of business, then maybe just try to make a deal rather than sell the business?

FWIW I'm skeptical about any % coverage claims, because nowadays a large portion of traffic is encrypted. So unless you have cooperation from the browsers (e.g. a browser extension, or a certificate installed to allow MITM), you cannot calculate the denominator.