Why not make it like a brandable affiliate or a brandable reseller?
Brandable affiliate is simply that they can change the colouring, logo, and name/company name - and get what ever commission they earn (but you do the billing). You could then probably charge a one-off/monthly fee.
Brandable reseller is ok too - you give them a cost price of your plans and they determine the retail price, coupons etc - all payments go to you, and they still get their commission. The system should be set up in such a way that they cannot sell below cost price unless their account has credit to be debited from. And from within it, they can change the header and the footer colouring, add a logo, etc - and the terms of use include their name/company name. Again, you could charge a one-off/monthly fee, but slightly higher since they can compete.
You could even have brandable reseller plus where they can create their own plans and don't need to use yours. As above again, but with a slightly higher fee.