I'm not sure about paintball, but airsoft can get pricey.
Heres a very rough absolute-low-end estimation for the items you asked about. The prices only go up from here.
Vest - $40-50
Primary - $300 (after taxes/shipping)/ $200 used
Mags - $25-40
Battery - $20-30
Charger - $40-50
Sidearm - $200 / $100-150 used
Mags for sidearm - $20-50
Eye protection - $50
Boots - $75
BDU (pant and shirt) - $50
As mentioned, this is a very vague estimate. You may find some stuff for cheaper if you get a deal on the classifieds. You may find some stuff to cost a bit more than what's listed here.
Add to this the cost of BBs and propane, along with the game fees as mentioned.
You may not have to get everything on that list right away. Most people build up as they play. Bare minimum would be Primary/Battery/Charger/Goggles. Boots should be in there as well unless you have a comfortable and supportive pair. You can attend casual games in cargo pants and a tshirt. One highcap mag could last you a round if you dont spray everywhere.
A lot of games also offer rentals. I'd recommend you try out before investing in anything. Games held in paintball places usually have a primary for rent (25-50 bucks, includes bbs and a mag or two) and provide goggles for play. You're best off trying it out and seeing if you like it or not before diving in.
If you do decide to get in, you'll have to get Age Verified to buy guns.
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)