You need to combine nBill with an ACL (NoixACL for example... a pain to setup but easily the most powerful & completely free).
Create two groups (Home Owners & Contractors) in your ACL.
Install the nBill subscription mod.
Create 2 new products (1 for home owners, 1 for contractors)
Both need to be subscriptions, so select yes for that field. Select the group they need to be placed in after registration AND after the subscription has expired.
For the home owners, select "free of charge"
For contractors, enter the pricing information
one off fee = a lifetime account (for example)
Create a new form. Add an option box and enter both the home owner and contractors group. Add a dropdown box, using the value and labels which relate to your pricing information. ('AA'=One-off; 'BB'=Weekly; 'BX'=Four-weekly; 'CC'=Monthly; 'DD'=Quarterly; 'DX'=Semi-annually; 'EE'=Annually; 'FF'=Biannually; 'GG'=5-Yearly; 'HH'=10-Yearly; 'XX'=Not Applicable)
So a value of AA would have the label of "lifetime account".
Change the payment frequency code to the field number from the form. Now test!
