membership/subscription solutions

Hello,
I tried to contact the WPeCommerce guys about this matter, but no luck. So I dropped their plugins as a choice for my online business.

I barely need some advice to achieve an ecommerce working as follows:

– date interval subscriptions: the user buy access to certain posts published within a certain date interval (let’s say July-Sept 2011). He cannot access private posts published before or after that period.

– The user can extend his subscription (or buy new ones) to access posts published before of after the date interval he already bought.

– Each private post should provide an unique per-user-per-post code. Such codes should be used as “member discount codes” to buy tangible products from the ecommerce.

– Possibly make this work with WP multisite feature (I need a multilanguage ecommerce site).

I thought WpeCommerce guys would help me choose the right plugins from their website, but they only pay attention to people who already paid them and I don’t want to buy random plugins only to get their attention…
Can anyone suggest me the best WordPress plugins to set up the ecommerce I need, or maybe script specific plugins for me (paid)?
Many thanks for any hint! ??