It looks like the 21108 LEGO Ideas Ghostbusters Ecto-1 production life cycle is coming to an end! The online LEGO Shop at Home site no longer has the set listed. Only LEGO Ideas products that are still available on the Shop at Home site include 21109 Exo-Suit and 21301 Birds. Several online retailers including Amazon America and Chapters Canada still has the Ghostbusters set instock for $49.99 USD / $59.99 CAD. Your local LEGO Brand Retail store may still have some available as well.
There’s a possibility that LEGO may get it again, but if you don’t have the set, you shouldn’t wait any longer as LEGO Ideas sets tend to get pretty pricey once the set has been discontinued.
Thanks to forum member fleury for the tip.