You are overestimating (by asking) the cost of fuel in such a worst-case scenario diversion that requires fuel dumping.
With this week's jet fuel price, 50 tonnes (approx. half of what is loaded on a 787 bound for a long-haul) would set you back \$31,000.[a] But,
A single flight diversion can cost Emirates anything from US\$50,000 to over US\$600,000, ...
On twin-engined aircraft the standard procedure for engine failure is to land as soon as possible. Since it is possible to land overweight—and aircraft are designed so that it is—delay to dump fuel is not considered acceptable, and no reasonable pilot would delay the landing when they can land already.
Landing overweight is not really a big issue. The ...
If you had an engine fire, even though it may be "out", you want your airplane on the ground as soon as you possibly can. You don't know what structural damage is lurking as a result of the fire. Dumping fuel would take a fair amount time to get rid of any significant amount.
So it's "Screw the landing gear. We're landing overweight".