Cost of owning a weapon in either sport is essentially the same, except on the low end - Canada doesn't really have cheap airsoft guns available that are gameable - whereas paintball does. But you get what you pay for in both sports, and in the end, it comes down to who's behind the trigger.
Ammo and gas are a big wallet hit for paintball. 2000 rounds is anywhere between $75(if you lucky) to $200 for 2000 paintballs - compared to $10 in airsoft. To make it even worse you shoot more in paintball due to the way games are played, and the fact paintball guns don't compare in distance or accuracy. Buying tanks and the CO2/HPA that goes into them is another cost that airsoft doesn't have to deal with.
I personally got into airsoft due to the different kinds of games played, I like a realistic objective based game. I thought airsoft would be more realistic - and it is. With paintball you clearly have an advantage with a $2000 set-up VS a 200$ set-up.
Airsoft isn't nearly as bad. Although I'm not at all a fan of people running around with stupid ROF's...I mean, if the gun your holding shoots 650, 800 SPM as a real-steel weapon; why do you need to throw a li-po in it, switch out all your internal wiring for stuff made from a heavier gauge, in order to to make it a super-high ROF gattling gun.
I've yet to see anyone post this as an issue taking away from the realism of the sport, and I'm not sure why. I think exceptionally high ROF's are for donkeys. I personally like to take out opponents with single shots and short 3-5 burst fire as well - again - its not realistic to dump a crap load of shots in a single burst.
Realism is the aim of this sport, is it not? Of course real bullets are far more effective than BB's are, they don't get stopped by brush, pushed by wind, carry further, etc.
but where do you draw the line? Does no one else have an issue with the ROF some guns produce?
Honestly that's what turned me off of paintball. Semi-auto back in the day meant semi-auto, and I used to love playing; but the way guns are made these days nothing is realistically semi-auto. +20 bps? Not when each shot is costing me 5c-10c, nooooo thankyou.