KLO, keep your eye on Craigslist. That's where I found my four Rocketeers. I don't know how "north" you are in NC, but I'm in the Raleigh area and that's where I saw mine. Of course, a couple of them I had to drive out of town to get, but still. And if you're close to Virginia, check the nearest Craigslist there.
I've seen 300, 401, 403, 500, and 503 machines on Craigslist over the last several years. I also bought a vintage Kenmore for a friend that needed cleaning up (the machine, not my friend). And to tell you the truth, I really liked that machine.
I've never sewn on a 300 or a 401, so I can't answer if they're better or not.
If you're ever down this way and want to see a 500, let me know. A friend of mine owns a costume shop (I do mending for her), so we could meet in a public place. If you've ever been on the shop hop here, her shop is in the same shopping center as Bernina World of Sewing.
Tate