We are in Rainham Essex and we have MB400 at £65 per bag
WINTECS sell DOWEX resin @ 69 + vat & free next-day delivery on any order over 30 quid.
I personaly would only use purolite resin in an emergency, it's rubbish, once it hits 001 its spent in a day raising the tds very quickly.
Dowex, on the other hand will last for longer + it will hold a low tds for ages, & i mean ages. I've personaly tested the two brands back to back & can honestly say the dowex is far better by a long way.
For a DI-only set up using 2 x DI vessels & dowex resin will save you a fortune.
tony