Buying paintballs from anywhere other than in person means you are paying for delivery in one way or another. It will come by courier and the survival of the paint is dependant on the packing and the handling by the courier
Buy in person and you prevent the risk of courier damage but you still have to do the transporting and storage
The question is why do you want cheap paint?
To beat the prices of your local site is impractical - would you be allowed to use it?
For an event etc you can get the best vfm on the day (or preordered) from the site traders
Cheap paint will be 'less good', the only way you will make a significant real saving will be by buying pallet loads
For the cost of paint look up the paintball shop sites, EG £30 or £40 a case