^^ Edit: like he said a stir plate isn't required. It just maximizes the amount of yeast growth. If you shake often enough it's not too much better.
Do you plan to go to all-grain anytime soon? If yes I'd say go for the full boil since you'll want all that stuff (propane burner, wort chiller, big-ass pot) anyway for AG. If no, I'd do the starter setup. I really noticed an improvement in my beers when I moved to making starters. Whereas for extract brews I really don't think full boil makes THAT much of a difference.
Look at the stir plates on the William's Brewing site. They are $60-100 cheaper than most places and mine works great. I think my starter shopping list was something like
1) 2L flask
2) Stir plate
3) Stir bar
4) Fermcap or another anti-foam thing
5) yeast nutrient
and it was well under $100. Keep a bag of DME around to make starter wort and you're good to go.