Custom Wordpress payment plugin

We need a Wordpress plugin that basically will password protect a certain part of a post, the same way as the “more” tag marks where you have to click on a button to read the entire text. We know that Wordpress has something a little bit similar, but it is not really what we are after. When the password tag (called pwd) is inserted in the post, two fields will display, one required (the password), and one optional (the e-mail in case the customer needs a receipt). And of course there has to be a submit button there to process the password. When the password is processed, a control routine is activated checking if the password is correct or not. The stored password is remotely located, but you may just add a local dummy password in the control procedure, and we will fix the rest regarding the remote part. If the password is correct, then display the rest of the post located below the password tag and send a recipt via e-mail to the user saying "this is your receipt". If the password is wrong, then display an error message and keep displaying the two fields. In the administration, there must be a process log (for those who used correct password) that displays password, e-mail, process date and time, number and post_id (id of the post where the pwd tag is placed). “Number” is a variable that the password tag takes. For instance in the post, the password tag can look like this: pwd[30]. Then it means that the rest of the text is not displayed without a password, and that the number 30 will be stored in the log together with the other process information. Also display the number together with the rest of the text if the password is correct. And finally, the number has to display in the post before the process (together with the two fields). We hope you have a development environment for this plugin and a demo site where you can show us the plugin in action. The plugin will be used on WP 2.3. It is not required to follow the Wordpress standards, but prefer that this is done as much as possible.