What is the best way to set up special pricing for particular customers?

We currently use IC/Edit Item/Pricing/A,B,C,D,E to set the discounts for particular groups of customers. For example, a particular buying group are all set to customer type A and therefore get discounts on the items set up with a discount amount set in A in IC/Edit Item/Pricing/A. This works for up to 5 buying groups (A,B,C,D,E).

How can I also set up personalized pricing for other customers? For example, Joe's Store has an agreement with us to buy his widgets at a $15 instead of the regular price of $20. Sally's Store buys another item at $20 instead of $25, etc. We have dozens of individual scenarios like this. Everything else these customers buy at our regular price. Regular pricing changes daily as new product is always coming in at new prices.

So I want to set something up so these customers will get their special pricing on the few items we've agreed up, but regular pricing otherwise.

We've never used IC's alternate price lists so I'm not sure if that can help us. Can someone steer me in the right direction?