Hi,
Thanks for the bug report. I confirm this as a bug, the product list was not correctly using the selected site currency to format the price, the Purchase.aspx page was correctly using the site currency. So what was happneing was that the product list was using the user browser language to format the price and then when they click the button to continue it would change because then the correct currency culture was used to format the price.
I have just fixed this and uploaded Site Membership Pro 1.0.0.4 with this bug fixed so that it uses the correct site currency format in both places. You can download the updated package from your purchase history by logging into this site and click the "My Account" link at the top, then click Order History.
Best Regards,
Joe