Yahoo Finance had a good service that allowed you to download share prices. Unfortunately, it seems to have been acting up lately, and is going the way of all things Yahoo, namely downhill.
The good news is that Mathematica can download share prices. If anyone is interested in learning how Mathematica can be used as a portfolio tracker, then let me know, and I'll do a write-up on it.
I'm very happy that Mathematica is included in the Raspberry Pi distro. I hope it continues!