Urgent small Drupal Rules configuration job

Hi All,

I've got a small but urgent job setting up some business rules for a Drupal (6.16) site using the Rules module. I don't need any modules designed or modified, nor theme tweaking, site installation, etc. Just some configuring. While this primarily involves the Rules module it also interacts with the CCK and Pay Per Node (PPN) modules.

The scenario:
I've created a "business" node type. It has a bunch of CCK fields, one of which is Business Listing Type. This field has 2 possible values, 1|Free and 2|Paid, and defaults to Free. I'm using the PPN module to enforce creation of this node type - sort of.

I want to allow any registered user to create business nodes, BUT only "free" businesses. If they want to create a (or update an existing) business node as a "paid" business, I want the Rules module to first verify they have enough PPN "credits" to do so.

If they do have enough credit, I want the node create/update to go ahead and the PPN balance to be decremented.
If they don't have enough credit, I want the node create/update form submission to halt with an error warning them that they have insufficient credit for this.

In my mind it sounds simple, and Rules appears to be able to do it, BUT I haven't been able to make it happen. Time is of the essence here so ideally if you were considering taking on this project you would be well versed in Rules use. It should go without saying that I want no hacking of any Drupal core or 3rd party modules - nothing but theme hacks, and only if REALLY necessary.

I'll be guided by enquiries at to what is a fair compensation for what should be a job of only a few hours for someone who knows what they are doing.