$11 Semi-Auto W/ Initial Tank of Air
$4 Full Face Mask W/ Goggles - Mandatory
$11 All Day Air - This is optional, I believe you can pay per fill
$3 Loader/Hopper Rental - I think this comes with the gun rental.
$1 Barrel Bag - I believe this comes with the rental as well.
You're looking at a minimum of $45 without the paint. That usually costs about $30 for a case of the cheap stuff and as mentioned before, you can probably split that with someone else, and be okay for the day.
The pain from being hit varies. It depends on where you're hit, how far away the shooter is, how fast the marker is shooting, and how much protection you have on.
Rentals usually come with a mask and full gun and a bit of paint( but not enough to last a round or two ).
As far as getting hit, it is just enough to make you think. You wont fall dead from one hit, but it doesn't exactly tickle. Getting hit on the hand/fingers does hurt though. You can't really freeze paint anymore, one half of the shell gets super soft and they break in the barrel.
Pain is relative. What hurts for me may not for you. Generally if you're doing it right though only your head should be sticking out, and if you get shot in the mask...it doesn't hurt at all. But I wouldn't recommend you getting shot in your sack.
For anyone thats never played before, wear really good shoes with traction, paint is slippery as hell, and wear clothes that cover your ENTIRE body (not a good day for booty shorts and a tank top), is easy to run around in, and that is somewhat padded, yeah its paint but it hurts like hell even still. DONT FORGET TO WEAR SOCKS! OH and wear a beanie type hat, I'm not sure if the masks you guys are gonna be wearing cover your ears, getting shot/grazed in the ear hurts really badly. Thats all the advice I have for the 3 times I've been lol