Make sure you have at least one PCI slot to spare. If your server has only two PCI slots and those are filled with a network card and a SCSI card, you won't have the ability to expand using another PCI card later on. In a dual-bridged PCI design, you shouldn't place heavily used EISA cards in a PCI slot, since this will cause a large degradation in performance of the PCI cards on the secondary PCI bus. Although legacy EISA cards can be phased out, you can use a low overhead EISA card, such as a remote management board, and then use the secondary PCI bus slots for network cards. The initial cost of the server is actually only a fraction of the cost you'll incur in supporting it.
Management software can help reduce operating costs.
HP, for example, offers free support only during business hours. Compaq and IBM have free 7x24 support. Others, such as HP and IBM, have their own support mechanisms worldwide. If this is a concern, you may want to discuss it with the vendor early on. Finally, take stock of the server's warranty.