Thanks for playing! I did have a few other people say that to me, but I couldn't come up with a solution in time for the jam. (Any ideas are welcome if you have any!)
Totally fair, ours dosen't have half of the content we prepared ahah
My 2cents: Maybe plan the enemies as hordes (since you have the bosses too) and open the shop automatically after beating one, like in Vampire Survivors when you level up. It's less flexible maybe, as you can't upgrade on the fly, but it puts more stakes on reaching that milestone and gives you room to think