Note that the oversized 4G expansion card that was being discussed some time ago reportedly has working (and shipped) prototypes and is now on preorder for about 170 GBP:
https://store.liberatedsystems.co.uk/product/opencom-lte/
(It only supports 4G, and looking at prices for 5G modules it doesn’t look like this is going to change any time soon—even 4G modules are 60+ USD in small quantities, and 5G ones are several times that.)