I advise the Gold Edition. I got it for £7.99 back in August 2006. Probably about...$14-17 or so? So, you should be able to get it cheap these days.
The patch for Gold is the 2.01 patch, and all you do is delete the old .exe and copy and paste the new one in it's place. Or just copy and paste over the old .exe, don't think you need to do any deleting.
EDIT: Using the currency convertor online, it works out at roughly $15.65.
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