When I worked for manufacturers, the generally accepted internal value that needed to be amortized into projected sales was $20,000 per line item for UL listing. maybe a little less for devices that had no protective function built-in. In other words when we in Engineering proposed a new product design, accounting assigned an NRC ( Non-Recurring Cost/Charge) of $20k per line item that needed to be recouped in the first 2-5 years of projected sales. They would take that to the Sales Dept for projected unit sales volume and then split that up as part of the unit cost that went into the pricing structure. So if Sales said they could sell 10,000 units, the UL cost was only $2 each. But if Sales said "We can sell 100 units" then the UL cost was $200 each and that would affect the sell price greatly. It killed a LOT of great ideas...
That's why I always laugh at people who look at some small device and say "I could built that myself for 1/10 of what they want to charge for it!" but they have no clue as to what it costs to attain (let alone maintain) UL listing.