Not exactly sure where you buy Tide...
But here, at both Super-Target, and Walmart, Tide is $11.99 for a 100oz, 64 Loads Bottle. The 50oz container, with 32 loads is like, $4.99-$5, although I've seem them mutiple times on Target Clearance for $2-3.
The last time I remember them "reformulating" there Liquid Tide was back in 2007, when Walmart told P&G to make there stuff 2x concentrated, or they'd be Gone for good. Powder Tide was made more concentrated back in 2010 or so, (again, at the Request of Walmart) besides that, I really haven't seen any difference.
One does have to remember, Tide is a TOL (Top of the Line) Detergent, and is very well formulated to tackle stain removal, plus Procter & Gamble spends a LOT of money marketing it. I think, if P&G actually didn't market there product, we'd be able to purchase it for a much better price, but... I do think there is a added cost for the actual ingredients they used to make it, vs other brands..
Now, I'm not saying that Arm & Hammer isn't any good. I've used it before, and thought it was good, but, it definitely doesn't have the Enzymes or Cleaning Power of Tide or All, and I really wouldn't expect it too either.
Personally my Favorite Liquid Detergent, is All Small & Mighty (the Oxy-Active one) and it contains enough Enzymes to do a really good job. Wisk is also a really good brand.
I do personally, though like to keep Liquid Purex, and A&H on hand for cleaning Bed Sheets, and the like, as I don't want as much Enzyme & Other ingredients being used on them. Pretty much just the Base cleaning surfactnats and nothing else
