Thanks all. Good suggestions.

1- I just downloaded Google Maps offline.
2- I was able to lower the GPS cost by switching to Sixt. It's now $10.33 per day. Europcar prices were insane. Still high but surely less than buying a Tom Tom I'll never need again. I still may cancel the GPS rental - but at least it's more palatable now.
3- I may just go the old school printed map route for $10 or so. I wonder though, where would I even buy one, lol. Unless it's at Glasgow airport when I arrive, I'd have no idea.