The most important thing in paintball is your equipment and safety.  There are many gadgets and gizmos used in the sport of paintball, but the basic equipment is all you need.  First of all, you need a gun.  A first time gun should be around $80-$160.  Guns may come in packages that may include a mask, gun oil, adjustment kit, and barrel plug.  Sometimes you must buy each of these items separately.  The mask should be the cheapest one you can find.  These are usually $15.  Gun adjustment kits and gun oil are used to keep your gun in shape.  These are probable $5 together.  The barrel plug keeps the gun barrel closed for safety.  You may also consider buying a camo jacket and pants.  This helps for skin protection and a camouflage look.  Boots are a must.  You can't go running through the woods in tennis shoes.  A hat or hood is good for protection there.  The ammo for your gun can be bought at 1000 balls for $30.  Remember that some fields make you buy their own paintballs that are much more expensive.  That is the basic equipment needed for a beginner in paintball.
The more you get involved in paintball the more equipment you will want.  There are better more expensive guns, masks, and so on.  With so many add ons and cooler looking stuff, the sky is the limit.  There are paintball pistols, snipers, autos, mortars, grenades and so on.  The styles and designs of guns and masks vary with each company.  The price range for some equipment can exceed $2000.  That wraps up about it all for more advanced equipment.