There have been a couple of posts recently which included queries about feeding sugar syrup to bees.
From my limited experience they can get through this pretty quickly so a cheap supply of sugar really helps.
If you are a member of the BBKA you can get a membership card for Bookers, the wholsale merchants, where you can buy sugar in big sacks. I can't remember the price (and it does vary with special offers) but it certainly works out cheaper than buying 2kg bags.
Sally