northern lights and easy sativa

im about to start my first grow. i will be growing (or at least attempting to) northern lights and easy sativa. what size of pots should i start them in (to grow for about 2 weeks) before i transplant them?
and what size of pot should i transplant them to? i was thinking 6 gallons??
i dont want to spend 100s of dollars on organic soil and perlite, but i would like to get some pretty big plants.
thanks!

also, forgot to add that ill be starting them indoors, then transplanting them outdoors. not that that matters that much, just thought id let you all know.
thanks.