You might find a standard 305m drum is as cheap, due to being the most popular.
For Cat5(e), be aware of the cheap shit. As its cheap shit. And fails quickly.
Also be aware of what you are using it for, and especially what sort of connectors you want to connect to it - basically 2 types, infrastructure and patch lead. Infrastructure is solid cores, patch is multi strand for flexibility. You will find a patch multi strand will not reliably punch down on a connector designed for infrastructure, and vice versa.
Cat6 - you probably want to get someone in, or buy the exact length premade, if you are planning on running 10GE over it. If you're never going above 1gps, stick to Cat5e on cost grounds, and the fact its easily DIY'able.
Lastly, this is all assuming you are 100% internal. If going external, you need proper external variants. If going high on a building, you will need STP and maybe a lightning arrestor.