If you haven't tried using wild lacto, it might be a good way to save a few bucks. Those lacto cultures from the yeast lab aren't cheap. I'll make a starter of 2-3L, add dextrose to 1.040 or so, then add 1/2 cup of base grain. If you keep it hot, it'll be sour in a day. Pitch that into the wort, then the wort will be tart in about 24 hours, sour in 48, and really sour in 72. That the procedure I use on all my sour beers. I haven't used a commercial culture, so I can't compare the two, but my way works "well enough" for me.