red hat diving gets good reviews of his gear.
As for the system cost, a tank & fixing + hose reel is all you'd really need, you can just plug the trolley into it and start working. £400 should cover it.
Just remember that the tank needs to be properly secured to the van chassis, not just the floor. There were a couple of ideas posted a while back about securing a 50mm x50mm box section in front of the tank & one behind it and then using some 20 tonne ratchet straps over the tank. It sounded like a very simple but effective solution if done properly, and very cheap to do also.