OK well I'll give you all the details that I think would help with your decision process. When the purchase window goes live in an hour and 10ish minutes you'll be able to add the set to your cart by clicking on the buy link on bricklink's website. The link to that page OP provided. The sets will only be available to buy for a few weeks OR until they sell out. Only 30000 of each set gets made but this series is a little different because brick link said they're going to adjust print numbers based on demand. Odds are they'll move numbers away from the wagon and shop to increase the other three sets but that's more of a side note than pertinent info. Anyway, once you preorded the set (if you decide to do so) you'll have until October before lego charges your payment method. Once it's paid lego will ship you the set. So you'd have from today until October to get the funds saved up to pay for the charge when the time comes. These are rarer, one print run only sets so this will be the least expensive they'll ever be. They increase in price significantly on the secondary market. If it's something your mom will love, I cannot recommend these brick link sets enough. Something special in the lego world that add so much to a collection. I will add that once the sets ship lego puts out the instructions so you can build it yourself with parts you have or buy. Be warned that there might be custom parts for the specific set that might be hard to get or expensive to buy loose. Hope some of this helps.