Look for a instacart promo like this on your email, you may get 40$ off 100$, and simply order items that you know will be in stock ($50) and items you know they won’t be in stock (50$). Items related with CHRISTMAS/HALLOWEEN are most likely to be OUT OF STOCK. So. if they don’t find these items, they will mark it as oos, promo will and your total should be tax + tips and $ after 50$ discount.
If you are unsure, request dasher to remove items you don’t want. Good Luck! If things go sideways, just request to cancel the order. Let me know how it goes.