Every month's been showing 1% bandwidth use, which I assume is being rounded up.
We're allowed 15360000 MB. It will take a long time before bandwidth is a concern. Theoretically, we could get to nearly 10,000 members before we eat up our bandwidth but that would be if no one uploaded any more attachments and we had the same amount of guests. Even so, we should be able to handle 1000 members easily.
There are things that can be done such as not allowing guests to see attachments, allowing no further attachments at all, or reducing the size of attachments allowed. That shouldn't be a worry for years though.
I don't know if price and performance have been an issue, but you might check out
https://www.nearlyfreespeech.net/For lower bandwidth sites particularly, they are quite competitive. Other than that, they are one of the few hosting sites I've found that have almost universally positive feedback. On the other hand, switching providers can br a royal pain in the ass, so if there is no issue, it obviously isn't worth it. BTW, their pricing scheme is actually set on the "integral of (1/(1+log(x)) between your start data transferred and the end data transferred."

. This takes into account your entire membership tenure, not each month separately.