In the US, RoadRunner and WOW are <$50 for about 5+ megs down and maybe half a meg up. Lots of people I know run all sorts of 'servers', on their lines. Yes, these ISP's forbid 'servers' and 'proxies', etc in their AUP's. Though no one I know has ever been hit with the stick. They're all minimally running ssh, smtps, https, dns. Some are running the standard strong stuff: freenet, i2p, tor, gnunet. Some use bittorrent. A bunch download from rapidshare, etc. They've had no issues.
If your ISP takes a liking to your line via their ticketing system and you can't shake them through education or feint... it's time to cancel and for your 'new flatmate' to sign up for the next line/ISP. Wash, rinse and repeat in loop. Business class is about pricing, SLA's, resell, contracts and associated legalities and marketing. Not data transfer. Residential end users, even without servers, use way more traffic than business end users connected to the same fiber/coax/copper plant.
