Coupon code discount working functionality?

Hello,

Here is the full scenario for the site.

I have the product/membership which will be valid for the 1 year only. It will expire after one year usage.

Like my my membership plan for my products expire on 31st January.

Now any user purchase the membership/products before 1st June then the membership/product costing should be $100. And if the user purchases the membership/product after 1st June then the costing of the membership/product will be $50.

This is because the membership/products will be expire on 31st January and the June month purchaser will get let benefit of my product. So I want him to pay less for this loss.

So is there any coupon code or script will work for this feature. That I have to add it once and forget rest of my life.

Additionally if the membership plan expires on 31st January my already subscribed user will get an automated mail there membership plan is expire need to renew it for accessing the benefits of the membership/products for one more year.

Please respond asap.

Regards,

Minh