Thanks all the great ideas and support. I have asked the host about data recovery. I'm waiting to hear back.
The guy who hacked it, was gloating in an underground hacking forum, asking how much he can sell my member-base for. From that we have his Skype, ICQ and several websites he operates.
He's 19, from the US it appears. My host is also in the US. I'm hoping they'll assist me in taking this as far as I can legally.
We live and learn. I truly believed the backups were safe. The host told me that the server was locked down, inaccessible to the outside world. Then tonight they tell me that isn't the case if a hacker has access to the main servers. Jesus.
The fact my team are pushing me to start again, and the members are emailing with their support, speaks for itself.
I will keep you all updated with the developments and I thank you all once again for such thoughtful, helpful responses.