And then you can wait for the cease and desist letter to arrive, since none of H+FJ's typography.com faces are licensed for use on the web outside their service.
Technically, you may be able to, but legally, the license doesn't allow for it.
The price for "serving it yourself" on the web is not listed: if you serve it yourself, more than 50 computers will be able to download it!
I don't think there is a price for "serving it yourself on the web"; outside of a small number of early beta users, the professional websites you saw using H+FJ fonts were probably using image replacement.