The cost is not an issue, it's the gangbang tags.
Double the costs if need be, but remove the gangbang tags.
Perk planes should be fun to fly, afterall thats why we're spending perks to fly them. The cost doesnt matter provided flying the plane is fun in the first place. The tags remove any chance of having any fun in them.
The f4u4, 152, spit14 are all excellent planes, which can compete on equal terms with the best of the free planes. They do not dominate the free planes. They are good planes, that should remain perked, but they shouldn't have to deal with the gangbangs brought on by, and only by, thier tags.
Comparisons between k/d ratios of free and perked planes is irrelevent. I bet if you perked the la7 and p51(not saying they should be) they would have k/d ratios similar to the f4u4/spit14/152.