Affiliate Tracking System

We need a basic Affiliate Tracking System for a site that is selling 1 item. We want to allow up to 2 tiers. If an individual wants to sign up as an affiliate, we need to be able to track their sales/commissions (i.e. 15%). If a company wants to sign up as an affiliate, we want them to be able to sign up their sales reps as affiliates. In this case, we would need to be able to track the sales reps sales/commissions as well as the companies sales/commissions(i.e. 10% to sales rep, 5% to company). Would also like to be able to set commissions based on volume sold (i.e. after a rep has sold 100 items, his commission would increase by 2 percentage points, 200 items increases by 2 more points). Will need reporting capabilities and ability to set price, commission percentages and volume/percentage point criteria. Automatic payment processing may be an option as well.