ZiiCube is by far the best for large orders, because shipping (per kilogram) goes down with more overall weight. There's no such thing as "free shipping", EVER. Stores that offer free shipping include the average/expected shipping cost into the item price, on the assumption that the average customer buys only 2-3 items. So, a purchase of just one lightweight item will be cheaper at Cubezz, but some 3 kilos of puzzles will be cheaper at ZiiCube.
Also, ZiiCube has a bulk discount - 2x copies of the same puzzle are sold at a lower price, 4x copies is the next discount tier, and 6x is the next one.
Most importantly, ZiiCube has a "VIP user" system. After you make about $60 worth of orders, you become a "VIP user" where you buy puzzles for "2x" prices even if you buy just one, "4x" prices if you buy two copies, etc. This, combined with shipping on big orders, makes ZiiCube by far the cheapest.
It's a good idea to take a small "loss" on your first order of about $70 in value or so, as a "non-VIP user", even if you can find that item a bit cheaper at i.e. Cubezz. If you plan to keep buying/collecting, that "loss" will very quickly pay for itself with future "VIP user" discounts.
But, RIGHT NOW, with the pandemic, they have a sale where regular (non-VIP) users get "2x" prices (the same as when buying 2 copies of an item), and VIP users get "6x" prices instead of "2x". The shipping rates have gone up for some countries due to the pandemic, and this sale supposedly compensates that.
Bottom line, don't buy the examinx from ZiiCube right away. It's not gonna get sold out in the nearest future. For a regular/new user, it's $248 + 1.8 kg of shipping. For a VIP user, it's $220 + shipping.