Water bottles cost a fair bit. You also need to check that the ball bearing is not stuck, and refill them daily.
A cheap alternative is to use large 2-litre tins (I got some from the local takeaway shop). If you make a small hole just below the rim you can wire the tin to the wall of the cage. Old lunch boxes work well too.
Another option is an automatic water system where pipes run through each cage and are connected by tubing to a large bucket for a reservoir. This works well if you have your rabbit cages in a shed or in a long line.
Whatever system you choose, check the water daily, and clean waterers out weekly.