Like anything else,
ebay sellers can ask anything they want for an item. It is the prospective purchaser that needs to determine whether the price is fair before bidding. You also have to consider the costs involved in marketing, providing and shipping the stamp(s) to an interested buyer.
Precancels and perfin collecting are both specialties and unlike non-precanceled stamps, there are some collectors who would pay a premium for a particular precancel town or type just to complete a collection.
I don't think the value of common precancels or perfins have dramatically increased in value lately, however the days of any stamp being valued at $0.01 to $0.05 have gone by; as any stamp -- even the most common ones -- are valued higher these days for the very reasons recited above.
Of course, in a package of kiloware these stamps are still probably valued at a penny or less, but if one has a need for a specific item, some collectors would be willing to pay a premium to get it.