There is a LOT of differences in chairs.  Yes they cost way too much.  So does a trip to the back doctor.  25-30 years ago when I sold office equipment the lady who specialized in furniture told me if a chair was to be used daily not to sell one that cost less than $175.  The customer would not be pleased in the long run.  That was in 1990 money.  So today the same rule would probably be $250-$300 or more.