First, that dealer's quote is ripping you off BIG TIME!! A brand new alternator (not necessary) is only $700 and 1 hour to replace. You can get the alternator rebuilt at a local rebuild shop for about $150.
The battery is $60 at AutoZone (Brucelee got one for <$40 at Costco) and 10 minutes to replace (1 hour min labor charge).
What's wrong with the top? There are better replacement tops from GAHH with a glass window for about $2K installed.
If it's out of warranty, you need to call a tow truck and take it to a local Porsche specialist and not a dealer. They will treat you more like a human being than an ATM machine. If it's still under warranty, they need to replace it all for free.
A local P-car specialist can take the alternator out, have it rebuilt, put it back in and replace the battery without Porsche being printed on it for a little more than what you were quoted for the battery. If you want to DIY it, it's very easy and will only take you two hours max since it's your first time doing it. I'll be glad to give you instructions to do it if you're interested in the DIY route.
Good luck!
