Forget Virtualisation - Embrace Cloud
A nice fat Server + VMware will cost more than your dozen or so desktops - virtualisation stacks up with higher numbers than this.
I suggest you look at Google Docs or similar - then your office suite becomes available from any device; an old PC, a tablet, a new PC, a shared PC. Perhaps not all employees need access to a PC all the time, perhaps you only need 1/4 Desktop PCs and share the facility among staff. Perhaps some need a PC, others can access docs using the tablet device that they already own?