If you want someone to take a quick look and give you a rough estimate with nothing on paper and no come-back, then yes, it is expensive. If however you're looking for a professional (with indemnity insurance) to carry out a comprehensive assessment, then it is going to cost in that ball park.
The only way to be sure is to get a number of quotes from suitably qualified and insured professionals. As asdfg eludes to, if corners were cut in the roof, are there other issues lurking under the surface?