*sigh*
A regulator is a device that consists of a chamber, spring, and afew other "secret" parts that every company has different.
What it does is it takes a certain amount of air in, which is regulator by the user, and inputs almost an identical amout of air into the marker at everyshot. This is used for your FPS to be consistent, and shots to go to approximately the same spot every time you fire your marker.
The regulator goes infront of the trigger frame, and is used as a fore grip, and is held by the hand which is not used to press the trigger.
All markers can use a regulator, not just high end. They are a VERY good device, but can be pricey, which is why many low end players dont use them. But if you use HPA, it should be a top 3 upgrade on your list.
They can be purchased at all stored, and all online stores, but i recommend
www.xpaintball.com Cheap prices, lost of choices, and cheap (sometimes even free) shipping.