What OS are you running? If the main storage is on the network, chances are the OS can run from anywhere.
- get a 100GB HDD from Craigslist for free or a few bucks
- any old crappy USB stick.
If you still want to go for PXE, you don't need any fancy networking. All you need is a DHCP-Server and a TFTP server with a Kernel and an initramfs. I think DNSmasq can handle everything with a bit of configuration. Or you go for a full server provisioning tool like Cobbler or theforeman
You assign each server their own image by placing the file in the directory /var/lib/tftpboot//Kernel
(something along those lines)