I tend to buy mine on site as I use bio bb's (which is what they use) a 1kg bag of .25 or .28 costs me £12 a bag. I've got a 1 litre pop bottle of .28 & I use 2x 1 litre pop bottle for .25 & as I'm going Sunday, I'll be buying a bag of .25 as I'm running low
For cqb, I use .20 or .25 non bio bb's & a bottle of 1000 will last me a fair while. I've got about 4000 left at the moment