I live on Oahu and have my groceries delivered on a regular basis.
Instacart will deliver your order from Costco, Sam's, Safeway, Time's Market, and Foodland. The latter two are local markets with Time's Market catering to the 50+ crowd and Foodland catering towards a younger, hipper crowd. If you order from Costco, the Instacart online price is about 20% higher than in-store prices. Sam's has a slight markup as well but much less noticeable than Costco, maybe 5%-10%. There have only been a handful of times when an item I ordered has been out-of-stock.
Safeway runs its own delivery service separate from Instacart and you can usually find a $20 off $70 coupon plus free delivery. I have yet to try it.
Shipt is Target's shopping service and will deliver groceries. However, it has been my experience that about 20% of the items I ordered online will be out-of-stock and I will be offered more expensive substitutions. Also, my orders almost always arrive anywhere from 30-120 minutes late even though I order 12-24 hours ahead - this really irritates me. However, the online prices are the same or even cheaper than in-store prices.
A little off-topic but if you want to order poke, Time's and Foodland are the way to go. Safeway and Costco's pokes are ok, but they don't cut the fish as well and the fish to toppings/other ingredient ratios are off. Too much "stuff" and not enough fish! Sam's has good poke, but not as food as Time's or Foodland imo.