Alright, I thought I explained the math already pretty thoroughly, but here it is one more time:
You get 20% off Creator sets, so for 31109 that makes $79.99.
You need to clip a 10% General Merchandise coupon in your mPerks account to get another $8 off to make the total $71.99.
As I said before, I had made a Gift Card purchase of $500 the previous day, which netted me the maximum of 10x$5 in mPerks rewards ($5 off every $50 in gift cards). I used those to bring the total down to $21.99
That $21.99 counts towards your total for the "For every $100 you spend on toys you get a $15 reward" mPerks promo. So depending on what you are buying, your purchase might trigger one or more of these rewards.
Then there is free pickup which applied to my order, so I picked mine up from my closest store. There is also a free delivery on $40+ in LEGO mPerks coupon, which can be applied to your order if you choose delivery. I have no clue if you need to tip or if there are any additional charges.
As you can see, it takes skill to play this game. I honed my skills with Shop Your Way over many years. Not for the faint of heart or the short on time. Elbow grease required. But worth it for a personal build for me.