hi
£6 per 100 is about the average price for a site fee for punters,
i wouldnt take your own paint bcause its garuntted that you will be noticed, this is either by a marshal catchin you filling up with paint, differnt colour fill or shell to the paint the ites using, i work at a site as a marshal and we spot people using differnt paint easily. some sites may allow you to take you own paint but itl be at a fairly high set fee.
dont forget that with entry price and paint cost the site owner has to pay for maintence, marshal pay, equipemt repair or buying new, resources i.e electricity or c02 everything liek this has to be covered before any profit can be made which is why there is a high fee on paint.
With paint your buying do you no the quality of it, as the site paint may be better and prevent hassel of breaks or even inacuracy.
before you take you own paint make sure your aloud as its like taking your own beer into a pub. Each site will also have their own way of dealing with people taking their own paint, you may be kicked of for the rest of the day or simply have your paint taken off you until you leave the site.
so just check before you take it and make sure its ok, or have you thoguth about walk-ons were you tend to be aloud to take your own paint (i think) or even joining a team were you pay £X per box (which tends to be decent paint) and have what id say as more fun then just atending punter days.
hope this helps
will