Simple webform with payment module what I need do is not an ecommerce site.

On my drupal website I need a simple web form with a payment (by paypal) and a node reference field prepopulated (by the entity refence and entity reference prepopulate modules).

The scenario is this: 

I have a content type called Team.
Only the admin can add nodes for this content type.
This content type has field of type user reference (by entity reference module). This field is empty to default.

Now, when an authenticated user visits one of this nodes, he can click on a link Administer this team!.
If he click on this link, he go on the payment form and it set the referenced node field to the clicked node id. Now with the payment webform he can pay.
The price is always 49 Euro, so he doesn't need set it.

After the payment I would like set an action (by rules module) that fetch the user that pay, the referenced node and set the user on the user reference field on the node.
In this way, trough the nodeaccess_userreference module, the user can start to administrate his team's page...

Hi tried to do this with the payment module beacause this has a good implementation with rules module, but I don't understand how to do a simple webform (at the url www.example.com/pay-your-team) with the reference to the node and without allow to the user change the price.

Can you help me?!

Thanks a lot!
You need to create a custom module for this.  You'll have to learn how to use PayPal's SOAP requests and handle it that way. 

This question, as it is now, is FAR too broad in scope to answer in this forum beyond that though.