The 1MB per minute guideline is at the average-sounding data rate of 128 kbit/second. If (like me) you like your MP3s to sound better than that, you rip at a higher rate e.g. at 192kbit/second, it's about 1.5 MB disk space per minute.
These days, phones can also do the job of MP3 player: my portable player is my HTC S620 phone with a 2GB card and Bluetooth headphones. You might not need to buy a separate box.
Watch out for the kinds of cheaper imported players you find on eBay - some are genuinely awful. I bought one with buttons that barely worked, and a 2.5mm headphone socket, which can't take standard headphones (with a 3.5mm plug).
