Here is what I have found to be a pretty good way to go that won't break the bank.

For an organization this size I use Backup Assist (http://www.backupassist.com). It leverages Windows Backup and has agents for Exchange and SQL.

I then break things into three categories and treat each slightly differently.

Level 1
The things you call critical such as active email, source code, CRM, financial data, etc.
This stuff gets backed up daily and depending on my level of paranoia (how screwed we are if we lose X days) I copy it offsite either to an alternate office or if none exists (your scenario) to either a hosted server at a datacenter somewhere (max on the disk and bandwidth and min on all else which is much less than you $750 per month) or to a server connected via VPN to the company principle's house (poor man's hosted server).

Level 2
The things that change often, but just aren't level 1 such as home directories, business shares and other data.
Data in this category gets weekly backups and usually gets posted monthly to a large USB drive which gets rotated with its twin monthly. The drive with the current data is brought offsite for storage (again maybe to the company principal's house or maybe a safe deposit box). When the new drive is delivered the old one comes back to be used for the following month's backup.

Level 3
These are the unchanging files like images, email archives and stuff.
You can either burn these to optical media (if you do muliple copies with one going to the company principal's house(s) and a copy to the safety deposit box if you got one) or you can lump this onto the USB drive shuffle.

Hope this helps those who might be looking for this kind of insight.