If a used gun in perfect shape is worth 1-2k then it is never pays to restock. If worth 2-4k then maybe. If a "family" gun then price is not the biggest issue. If you have more money than time or want a gun to fit and know they don't exist then do it and don't worry about the cost.

Truth is that most times it is cheaper to keep looking instead of taking on a major project gun. But no hobby is a money maker. If you break even you have done extremely well.