I've used BDS in Sheffield a number of times. £35 for a 3.5 tonne trailer for the day. Get it on a Saturday and the 35 covers till monday morning.
I bet most trailer places are about the same price.
I'd personally prefer to hire a trailer than borrow one. Less hassle, no problems if it goes walkies, and no worries about have the brearing been greased, or just watch the... if you know what I mean ;)