I'm a regular at our local Dollar Tree...I found sizing there for $1 (of course) and bought 3 cans; another amazing find there is Reynolds alum foil individual pieces, 25/$1.00. Also I buy all my "ziplock" bags there, sometimes I find the 2 gallon size which are great for projects.
Don't know the difference in sizing or starch; just have read that sizing is preferred on quilting projects....