A rule of thumb I've heard is 1x the last 12 months revenue. That is if the business is in good shape and has growth prospects. So if you're only bringing in $10/month, the best case scenario would suggest $120 for the clients (since they aren't paying anything).
That's completely off-the-cuff. If you want a more accurate evaluation, then we'll need to see the domain name and website.
Good luck
