What material size do you need to roll?
They can be got for sensible money if you arent looking to do anything over 16 gauge
Sorry, to do pretty much anything over 1.6mm (16 gauge) you are at a minimum of £1000
You could do flat bar through a ring roller, but again, anything from £150 for a crap one to well over 1k for a good one.
You could get a cheap ring roller and get some bigger rollers made for it to accommodate the 6" width you need, otherwise it is going to be an expensive venture unless you can make something yourself
what length of item are you making?
Could you put two blocks in a press and bend it that way
http://www.qualimach.co.uk/machines_fabrication_bendrolls.php
I cant find any reasonably price plate rolls, I guess you will have to make one or keep an eye on local plant and machinery auctions.