Which Server to buy?

Hi
I am helping some one, he need to setup a server in his 8 employees business. Currently all his 8 workstations are Workgroup. I am thinking about server 2008 R2. He might expanded in future. He only use 8 stations for now and will need a network printer. Which type CAL should he go for? Can I install server 2008 R2 on one of his workstation i5 with 64 bit, 18 GB RAM and 2TB hard drive? Or he will need to buy a severe which will cost him lots of $$. Do Microsoft still sales server 2008 or they only sale 2012 and above?

Thank you in Advance