Recently the prices of most spells were increased to an approximate value of 5gp per spell level.
This was a correct move.
But it seems that at least some of the "research only spells" were forgotten during this change. One documented example: Insipid Weakness costs around 6pp on this server right now (if you are lucky enough to find a vendor, who has it in stock). But the correct value should be around 17pp (which conforms to the spell level 34).
http://web.archive.org/web/200107240...ell.asp?Id=108
(The above site is btw also a very good source for classic spell prices in general)