I’m having a hard time tracking these down on eBay for an affordable amount.
Are these shrink wrapped in the stores? The ones I’ve purchased have the crates open but the droids are still sealed in blind bags. The sellers are able to tell what is each blind bag so hopefully everything is fully sealed in the stores otherwise they’re probably just picking the expensive ones.
The 4 that I bought in that parks had the wrapping around the base of the crates.
I thought that MAYBE the size of the bag in the crate would give some indication if the droid was an astromech or a BB unit, but that wasn't a clear enough indicator.
As for WDW? I only found the Mystery Crates in the Droid Depot shop inside Galaxy's Edge. They weren't even in Tatooine Traders at the end of Star Tours, and that is one of the better shops in the parks.