I have a use case in which I wish to collect payments before users are allowed to fill a form; basically the form is an assessment form for which the provider (offering analysis) would like to charge money.  

Currently I have the form setup using webforms, but I couldn't find a decent or well established way of collecting payment with webform submission. I already have Ubercart on the site so, if there is a Ubercart to webform bridge, I would definitely like to know about it as well (I couldn't find any). Lastly I am also open for any other approaches. 

My use case is the following.
Users pay for the assessment (service) using Paypal, and then they are given a link to submit a form; the submitted data need to go to the provider.  

Do you have any ideas on how this could be implemented? I assume it should be a relatively common use case.