Being a sculptor myself, this is an interesting question. From time to time, especially on projects that involve several figures at once or various film projects, I of course have had to hire sculptors to complete the projects. Sometimes, I'll just hire another sculptor I like to get their take on my design-- see what they can add to it. Some of my favorite sculptors to work with have done some amazing work for me. I sculpt most of what I do myself, but the most I've ever paid another sculptor for a 1/6 (or close to that size) head sculpt, was $600. Like Boris said-- quality is king.
I know people with hundreds of figures in their collection, I also know guys with a dozen-- in some cases, I think a smaller amount of truly phenomenal pieces, outweigh a huge collection that includes mediocre work. But that's just my opinion. I'd pay $1,000 easy to the right sculptor on the right project.
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