The production cost per journal in a small sample of 8 humanities and social sciences journals, as reported by Mary Waltham, ranges from $90 to $1,326 U.S. per page (online only, print costs subtracted). This is a price differential of close to 15-fold. That is, the most expensive journal costs 15 times more than the least expensive journal.
The actual variation in price is likely to be higher, as this is a relatively homogenous group of U.S.-based journals that are the flagships of their associations, with costly rejection rates in the range of 90%. Production cots could be significantly higher than average humanities and social sciences journals with more common rejection rates.
For details on the Waltham study, please see my previous post.