Help me finish: Discount for paid subscriptions

[luroca]

Please, excuse my bad English.

This hack allows to assign to paid subscriptions a discount for selected usergroups. It is a very requested hack and I was tired to wait that somebody writes it. The problem is that I don?t know to code

It has two ?minor? bugs and a very important bug:
Minor bugs:

1) The discount is the same for all currencies (dollars, pounds, euros). It?s only a problem if you have prices in more than one currency.
2) The format of the cost changes from (for example) $5.00 to $5 (without the .00) if discount is applied. It is an aesthetic bug.

The very important bug:

3) The transaction with paypal goes OK, the user pays his subscription (with discount), he receives his receipt, he returns to the forum but no subscription it is applied to the user or writen in the database. As the doctors say: the surgery has been a success but the patient has died.

Is this forum the correct place and somebody can help me with this hack?

Thanks in advance