if you have cwm install on the phone, you can use your browser and download the rom straight to the phone, and boot into recovery mode and flash the rom that you downloaded.
Or download the file to your computer, take the micro-sd card out of your phone and copy the the file to the card using a card reader.
Also, if they are charging $10-15 for the 2.2 upgrade AND it is coming on it's own micro-sd card, maybe they are not charging for the upgrade but for the card? Expensive card, but all the same...