You can buy 11sp Shimano 105 for pretty cheap right now ($407 shipped at Ribble.) You would need to pay somebody to install it. It would be best to negotiate with the shop you buy the bike from to get a discounted rate to install it. Basically you just say "if I buy this bike from you how much will you charge me to install 11sp Shimano 105?" and decide if it's a good deal or not. You'll probably need a new rear wheel too as most 10sp rear hubs aren't compatible with 11sp.