I do not plan to step in any stores, anytime soon, so I only order for deliveries.
I did 4 times with Instacart from Costco. I noticed for each individual item, the price could be 20% to 25%, higher than purchasing at the store, plus tips. I noticed other store prices for deliveries also higher: Walmart, Amazon Whole foods, etc.
It is the price we pay to keep ourselves a little safer.
I do not believe Walmart charges a higher rate for curbside delivery vs in-store purchase. I've done curbside a half dozen times now and in general love it.
Here's my tips:
1) If you don't know everything you want, do $30 worth of stuff to reserve a slot. You can always add to it or remove from it up to 1:00AM or so the night before your pickup time.
2) You can control substitutions on each item separately.
3) As with other services, sometimes things that were in-stock are no longer by the time you get to the date of your order. Be aware of this - I use this to influence my item selection, allow/not allow substitutions, etc. (see below)
4)Walmart's policy on substiution in general is to not rip you off. What I mean by that is if you order x, and x is $1.98, they tend to subsitute something of equal or better value. I use that to my advantage. For example, I will order somethings using the Walmart Value brand (i.e. generic) for example "Great Value Split Peas" and ALLOW substitutions. If they give me Goya, then that's OK with me!
5)Similar for large vs. small - I ordered some Velveeta (which I don't think I've eaten since the early 80's!) just to have some shelf-stable "cheese" (like) stuff. I ordered the 32 oz, Walmart substituted 2 16 oz packages - even better!
6) If you want a lot of something, consider ordering "similar" things. For example, they have Strawberries this week $1.56 for #1, $2.98 for 2#. I'm trying to get a lot of them as I want to dehydrate a bunch for summer hikes (given the good price). Since I'm limited to 2 of the 2#'s, I order both the 2# and 1# varieties. I've been using a similar strategy on meats - order a couple kinds of beef and turkey. Use what I can and freeze if needed, and just skip ordering some the next time. Also, I've been making some beef/turkey jerky so it doesn't go to waste.
Not perfect, but the strategy has been mostly working for me. I haven't had to go into a grocery store since the 2nd week of March.
p.s. If Walmart prices go up on an item, you still get the price when you added it to your order. If prices go down, theoretically you are supposed to get the lower price.
p.p.s. BEEF prices ARE going up. I happened to a 5# ground beef's in my order this week @ $2.796/#. I see on the web site that it is now $3.99/#. Glancing through other prices, I also see some increases. I'm doing some "organic grass fed" items (ground and strip steaks) as those prices are about the same as before (and thus not as much of a premium)
p.p.p.s. This post makes me sound like I'm a big beef/meat eater. Ha ha, I'm really not - most of my protein sources is not animal (but my kid loves it).
Hopes this helps someone...