If not, look for Penfolds Club Reserve port, Six Grapes port, or any inexpensive Cockburns port. I don't know where you can get these - the bottle of Cockburns we drank together way back when was from some now defunct .com startup - but BevMo might have them in a pinch. No idea.
[Updated 20 September 2003. I stopped by my local Cost Plus today while I was waiting for my oil to be changed, and they did have the Clocktower for $10, which is still a good deal. I'd forgotten about it, but another option would be the Sandemans Founders Reserve, although it's more expensive - about $16. BevMo probably has that one as well. Finally, the Six Grapes port is pricier than I remember at about $20 - it's probably worth that only if you really feel like splurging.]