Simple / manual back-end for a crowdfunding page (Wordpress or other CMS)

I'm setting up a crowdfunding campaign on a private webpage. This is the brief: - The campaign receives funds through PayPal with two levels of payment. - Backers receive, upon receipt of funds, in different proportions according to payment level: Membership of a private forum, a referral code that allows their backer account to accrue benefits (ie discounts on future products) when other people back the campaign and mention their referral code. - A backer who uses a referral code should also accrue a benefit for using the code. - A system to generate and manage these referral codes and member benefits. - A web forum I need the system to be as simple as necessary to fit within the proposed budget, prefering to use free plugins that already exist, for example through Wordpress or other CMS platform. It's perfectly acceptable for example that each backer would need to be processed manually and that their referral codes would be picked from a random number generator and input into a database which is manually maintained. Manual processing won't be a problem but there should still be a system designed for the manual process, and recommended tools to make this process easier. Of course the more the system can be automated, the better. 3rd party tools like Hubspot or Mailchimp might be used. I've chosen the $30-250 budget range but really this needs to be at the low end of that range. If you have any suggestions or alternatives, feel free to write a brief proposal explaining the benefits.