Yep. I think that will even be cheaper than getting a new SSD for the PS5. Does the PS5 have a second M.2 bay for expansion or do you have to take out the original SSD and slot in a larger capacity one? Because if it's the latter then ouch.
I am pretty sure they'll have a solution for an additional storage to be plugged in but it won't be as straightforward as the Xbox solution looking at the images so far. There will probably be a PS5 teardown next month to let us know.
It'll be an interesting one as Sony will be releasing a list of drives that will be supported and probably more importantly are actually able to slot into the PS5. It could go a lot of ways. Eg. Maybe the drives released that work in the PS5 are at first all £250+ drives? Alternatively a company could create one that is perfect for the PS5 and they manage to undercut the Xbox version... I expect this to be something that isn't worked out properly until well into next year, but at first I do expect Sony's solution to be the more expensive of the two and the most confusing for your average customer.
Edit: Although all that said, I don't think either company will be bothered about getting into a pissing contest over the price of additional storage. People will choose their console based on reasons other than an SSD costing £20 more or whatever. People will just buy the storage at the price offered regardless if they want it.