Amazon gives non-Prime members free shipping at $35 or more of eligible items. Instead of simply letting users get the product with free shipping, they’ve added a discount that prices it exactly one cent below the $35 limit, while only subsidizing the price with $3.38, which is about half of what they’ll then charge you for shipping.
IFixit is generally good quality/value in my experience if it’s actually them and not some knockoff/drop shipper. Granted haven’t had a need to buy anything of theirs for years because the one I have keeps being great.
That kit is $40 on their site. Weird that it’s cheaper on Amazon in the first place.