Just to chuck into the mix, Combat paintball i belive are opening there sup-air field very soon (we all hope) at Northwold.
Im under the impression it'll be open for there first Walk-on on June 5th.
Worth giving them a ring.
Also, to the query about prices, they usaully do charge at rental prices, however there first walk on they've priced as a £20 green fee BYO (or £30 for a box). Obv got the added extra of being able to pick up pyros there for some good prices (usally 4/5 for £10, pick from a range of smoke colours, flash, bangs and stuns)
Personally, played a good couple of fields around east anglia (havnt played apoc yet, but is next on my list
) and they seem to be a nice team of marshalls. They see around 300 people on there Summer Rental games (split into 8 teams, kings + queens torny), i can only hope there Walk-ons prove as succesful.
Sole