My first instinct on how to solve this would be:
Do you really need to see all those $0.00 values in your lookup field? Is it important to you to see all of those $0.00 values?
If not, just modify your lookup field to become a conditional lookup field by filtering out any records that have $0 as their value.
Oh, and I should add:
If seeing all those $0.00 values IS important to you, then I think the easiest way to solve this would be to simply create ANOTHER lookup field where you conditionally filter out the $0.00 values, and then base your formula on THAT lookup field instead. You can also hide that additional lookup field so you don’t need to see it.