No, we expect "superlative degree of ~" to be followed by a noun, not an adjective. You can say "costly to a superlative degree", though it is quite elaborate language, and not a tremendously common thing to say. g.
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No, we expect "superlative degree of ~" to be followed by a noun, not an adjective. You can say "costly to a superlative degree", though it is quite elaborate language, and not a tremendously common thing to say. More common would be e.g. "extremely costly", "extraordinarily costly", etc.