to be fair to the other activities, they're more priced on a constant half hour of action. Paintball sites tend to spend a fair chunk of time kitting people out, safety briefing, explaining games. The average player is lucky to see 5 or 10 minutes action at a time with a bit of hanging about in between times. if you play 8 games in a day that's somewhere between 40 and 80 minutes of trigger time.
Plus, do you really get away with £40? Buy extra pods and you're upping the price considerably.
Anyway, for regular players like who frequent our beloved forum, take the cost of paintball over a year including marker, tournaments, big games, training etc and it probably does work out expensive. Doesn't matter though, it's still more fun than anything else