I know that this will make me sound like an antique or worse, but I've successfully navigated around many parts of Scotland with nothing but a (gasp!) printed road atlas. Most recently was last year on a trip that included Argyll, Islay, Lewis and Harris, the far north, then back to Edinburgh via Dornoch, the Black Isle, Speyside, and Perthshire. All with Philip's Navigator Scotland atlas (mostly 1:200,000; 1:100,000 from the border to the Forth-Clyde line) for a whopping £8. So if you're willing to go low-tech, it can be done.