A Netflix cache appliance isn't dependent on the number of customers, it's on dependent on the amount of traffic from Netflix. You don't need 5000 Netflix customers, you need 5 Gbps of peak traffic to qualify.
However that isn't your only option. You can just peer with Netflix, they have an open peering policy.
However that isn't your only option. You can just peer with Netflix, they have an open peering policy.