Since you had mentioned finding an online Fancy Feast deal, I thought I'd post what I've found for prices (I'm new to having a diabetic cat, but I hate paying full price for anything so I'm quite the bargain hunter and couponer)...
Target: Twice in the past month, they've had a "Buy two Fancy Feast 24-packs, get a $5 gift card" deals" while also running a sale price (I think $11.99 the first time, and $11 the second time). So the net price was $19 and $17 for 48 cans, respectively, if you had no other discounts. However, in addition to those discounts, they also offered an extra 5% off through their Cartwheel app one of those times for even more savings. And then also on top of that, there is currently a $1 off a 24-pack of Fancy Feast coupon that is good until sometime in July. It came out a few weeks ago in the Sunday coupons, but you can find people selling them on eBay and other coupon clipping websites for pretty cheap. Realizing that a 24-pack was only going to last me about 8 days, I decided to buy a set of 20 of these $1 off coupons from someone on eBay for about $3.50. (I've already used 6 of them, so I've already saved more than I paid.) So...all together on that last Target gift card deal, for every two you bought, the cost after 5% Cartwheel discount and coupons was $18.90 and then you got a $5 gift card back, so the net cost was only $13.90 for 48 cans! You can do as many of these gift card deals as you want in a single transaction (buy 2 get 1 gift card, buy 4 get 2 gift cards, etc.); however, you can only use 4 of the same coupons at a time (per household per day, I believe), so if you were using coupons you would be limited to buying 4 and getting 2 gift cards each day, but the sale runs for 7 days and you can go back every day if you want. (Oh, and I almost forgot, if you have the Target RedCard credit or debit, you get another 5% off, and if you fill 5 prescriptions at Target pharmacy they give you a 5% off a total purchase coupon for yet another 5% savings...all of which stack so that could mean an extra 10% off the already low deal price.)
Walmart: I haven't found any sales or deals on Fancy Feast at Walmart yet, but their regular prices are the best non-sale prices I've found. Their 24-packs are $13.68, so if you're using those $1 off coupons, the price is $12.68 for 24 cans. However, they also have 12-packs of some single flavors for $6.42 (I know they have the Classic Turkey and Giblets and Classic Ocean Whitefish and Tuna, and I think they also have the Classic Chicken, but I honestly can't remember since I've mostly been buying the 24 packs.) So, without any coupons, the 12-packs are actually cheaper per can, but there are fewer flavors that come as 12-packs.
Grocery stores: I haven't found a single grocery store yet that has decent prices. I even shop at a grocery store chain that will double coupons up to $1.00 (for a total of $2.00 off) but their regular price for a 24-pack is $15.49 (!) so Walmart's regular price + coupon is still a better deal.
Pet specialty stores: The prices at Petsmart and Petco are generally higher than Walmart ($14.99 and $13.99, respectively, for 24-packs) but if you sign up for their loyalty cards, they sometimes send total purchase coupons (for example, 10% off your entire purchase) which can be paired with manufacturer's coupons. So if you had a 10% off total purchase coupon and also the $1 off Fancy Feast coupons, you could pick up 24-packs for around $11.59 each.
Online: The only online price I've found that is even somewhat competitive is through Amazon's Subscribe and Save program. The 24-packs cost $13.68 each (confirming that Walmart's price of $13.68 is probably the lowest price around and Amazon is price matching), but if you subscribe to a monthly re-order agreement you can get 5% off ($13.00 each), OR if you subscribe to 5 or more monthly products (looks like they need to be different products not just 5 of the same thing) you get 15% off ($11.63 each). Plus, you get free shipping on orders over $35. So, if you can find 5 products that you can subscribe to monthly for the same or better price than what you pay at the store, the Amazon multi-subscription price with the 15% off discount is probably the best price without coupons or other deals.
All in all, I plan to watch the Target ad for another Fancy Feast 24-pack gift card deal (if they've had two in just the past month, I'm guessing there will be more...) and supplement with 24-packs from Walmart if I run out before another good Target deal comes along.