Pricing structure

Just a quick question to those who know-

The free edition supports up to 3 users, and $12 a month after that. No problem, I understand that. but the buy now page lists "storage" options. Does that mean if my DB grows beyond 100 or 250MB that I have to pay essentially $30 a month for another 100mb of storage?

That seems a little steep to me, can someone please clarify. I can get a webhost for $5 a month that will give me a gig of storage, so how can 100mb be $30 a month?

Also, any idea on the pricing of the on-premise model? i can't seem to find it anywhere on the site. I would like to host it myself if the storage fees make it more expensive.