Can I get Mavericks by CD?

No, download only.

I don't know if that's the sort of thing they would let you do at an Apple Store. My wife stands outside our local one to back up her iPhone to iCloud because we don't have wi-fi at home. 5.9GB is a different matter though. 🙂 Still, they may let you.

We have been talking about buying new computers each, but we have to factor in the $400 per year upgrade to our Internet connection it would mandate in order to accommodate Apple now doing everything online.

you should use eternet. not wi-fi.

Wifi is fast enough, usually the bottleneck is the Internet connection into the home.

I don't have any problem downloading Mavericks-sized installers over wifi, but I have a very solid and fast DSL connection coming into the home.

Contact apple. Here (Australia) they will sell you a USB for $60 with mvks on it.