Cheapest way to change trans?

I am looking at buying a used 1995 ford contour. The transmission needs to be replaced. Should I buy the part and then take it to a local shop for it to be switched out there? How much would that run me(about)? Should I try to change it myself(no car experience but my dad can talk to me over phone as he was a master mechanic)? Or should I get both the switch and the new transmission from the shop and let them worry about a warranty? Thanks