Costs? Do you have; switches, servers, storage and network available for the DC side of things? What are you planning for the desktop clients, old kit or new clients? In short if you have all the infrastructure in place and this will not need upgrading for say at least four years then look at VDI in a box for basic desktops and cheap licensing.
The variables are considerable and you need to consider refresh cycles, maintenance, management time, power, etc to get the real OPEX and ROI figures.