For instance.................
http://cgi.ebay.com/Vodafone-a-la-Carte-Gr...1QQcmdZViewItem
Vodafone Greek card for sale on Ebay. There is a reserve and I imagine it is probably quite high. Just watch it rather than jumping in. You are in no rush, correct? My point is there are such things for sale. There are other internet sites that sell new SIMS and you should check those out, too. USUALLY, they are quite high. Some of them also offer phones.
As I said, our Greek friends may be of some help and provide an idea of a sane price to pay for a new or used SIM.
Look around the forum; there are others coming and going places and the advice is usually about the same.
On one of the German boards, they even have a SIM swap discussion where they loan out their vacation SIMs. I have not seen that here or on Howard Forums.
Stan