Jared Spool wrote an article about how to prioritize using a formula he attributes to Bruce McCarthy.
(Value ÷ Effort) x Confidence = Priority
“The beauty of Bruce’s formula is we can make this as simple or detailed as we’d like. A simple way to represent Value is 1, 2, or 3, for low, medium, or high.”
“We want to prioritize work that offers large value while taking a small amount of effort, assuming we’re confident in both our estimates of value and effort.”
“By itself it’s a meaningless number. However, when we calculate other design item priorities the same way, we can see what we should work on first.”
I think the 1-3 scale makes this workable. Quantifying actual value and effort would be ridiculous, but all you really care about is relative value and effort between tasks you are prioritizing.