Hi Rich,
There ARE options for you - I'm frustrated slightly as it's an area that I specialise in and I would LOVE to assist - however I'm going to be diligent and follow the forum rules :) (Although you're always welcome to PM :) )
In essence, I would talk to a business solution provider - either in the telephony or the IT arena - I would actually recommend telephony.
Not only will you be able to reduce costs massively on the broadband side, but you should be looking at other aspect of the solution - for example how voice is delivered (and costs reduced) to these users - I'm presuming they use the phone??
I won't recommend any specific providers - but I would recommend that you use a smaller firm who truly understand what they are doing - and not one of the big blue-chip firms (i.e. not BT/Talk-Talk/Opal or anyone of that ilk.)
Hope this is of 'some' help,
Jim