I am also looking for a Evelyne bag too, and here are the prices in Hong Kong (which I think is similar to the px in the US) (USD1=USD7.78, please divide the below amounts by 7.78, you will get the USD equivalent):
PM2 (with a pocket at the back of the bag, but without compartment pocket inside the bag): $15500
PM (with a pocket inside the bag, but without pocket at the back of the bag): $13100
GM (bigger size than PM): $14800
I will go for a PM, because it's cheaper, but outlook is the same as PM2. PM2 is designed for those who need a pocket outside for convenience (e.g. carrying mobile, tissue, MP3).
If you are very tall, you can go for GM.
TPM is too small and is not really that practical.
Good luck with your Evelyne hunting!