(looking at french actors)
there are many prepaid offers, but hardly one with data.
for instance with orange, 8 euros for 100MB (bummer) and even then it's data only, made for tablets and usb dongles. physical shops abound but I dunno if salesmen will be pricks.
even then once you cross the border you're "abroad" so it credit will dry out extremely quickly if it works.
one other offer does quite some voice and messages but a minute amount of data (for emergency looking of transport schedule or plan, I guess)
it's hopeless. except for that thing I've stumbled upon with google, with a somewhat decent price.
https://www.roamline.com/carte-sim-roamline
what's funny is, it's made for travellers but I could see myself using it, even in my home country
(pay-as-you-go data is dire here, at least for now)