Yahoo search perhaps? As you are based in Bristol, you know it ain't going to be particularly cheap around then. Guesthouses would be the way to go, unless you can get a good deal from Travelodge by booking ahead, maybe? Whatever you do, get in there quick. Coronation Rd guesthouses are very reasonably priced - if they aren't booked for then.

Would prefer hotel to guest house.. up to £65 per room per night.. Have found the marriott and thistle for this price but they dont seem to do triple rooms!

Try serviced apartments - quick search found Geometric Apartments - look pretty good and central? A 2 bedroom apartment is £100/night which would sleep up to 4 people