Define wildly expensive? If you have a BT line and can get normal broadband I would recommend the ISP I use
ADSL24.co.uk they do have caps but they are pretty reasonable ones, although it does depend how much data you want to shift during peak time. The 800k upload speed is pretty good too (I use the home service so I get 400k).
There are no blocked ports or any throttling or traffic shaping too which was the deal breaker for me.
Jen