Hello Tom,
it really depends on what they charge you and how many servers you want to host with them. But $7/GB is to high. We could offer you considerably better conditions than that and still make a decent amount of money :).
You should ask for remote hands support (and how much is included per month). You should ask for reaction times in case something breaks with your server (aka, how fast is remote hands available) as well as with their connection. Do they have backup connections, who is providing their connection, how well connected is this provider. Furthermore ask what happens if they or their connection provider goes out of business (not unlikely these days). Demand at least one month of notice.
As they will normally not state anything in their SLA that would make them pay you money, you should make sure that the risks are fairly low of something happening and that you have the option of leaving them quickly if they don't provide you the service (e.g. if the internet connection is down for more than 12 hours per month, then you have the right to immediatly cancel the contract without further notice).
Last but not least, you should make sure though that you don't promise something to your clients (e.g. uptime of 99.9%) if the hosting provider does not guarantee the same to you.
