Display group pricing discount upfront

Okay, I've played with the group pricing that is present in the default ZenCart installation and documented in wiki. It say (and it is true) that group pricing discount is applied at checkout. So even if I assign a customer to a discount group, the customer will not see the discount until checkout.

I would like to re-work the code so that it is possible to show this customer the discounted price as he/she is browsing the products (and not have to wait to checkout). What is the best approach for this?

There's no way for the cart to know if the customer is a member of a discount group unless they are logged in (so it can check against the customer_id). Your best bet is to take a look at the dual-pricing mod and look at how that module uses the customer_id to display lower prices (again, this can only happen when the customer is logged in).