I saw a SuSE enterprise in action a couple of years ago, there were not many differences at user level, but it had a lot of administration and monitoring tools. I saw a workstation being completely setup from blank disk to full integration in net environment in 10 min. I think if you have a large, structured or heterogeneous (ie winnt+mac+linux+sun etc) net, or if the topology often changes (many laptops), it's worth the money.
Instead if you have only a few x86 machines on a ethernet network, with a linux-only environment, or samba shares are enought for you, and if the core system won't change, than any 'stable' linux distro will make the job. Please consider devolving a fraction of the savings to a development project of your interest.