When upgrading a monster category, such as beast, the cost of 25 XP on the Spider Queen, is this 25 XP per beast or for the entire category?

leoj said:

RtL pg7
6. Monster Upgrade Costs
This section lists the XP cost for the Avatar to upgrade each of the three monster categories to the next level. For example, it costs the Titan 25 XP to upgrade his humanoid monsters from Copper level to Silver level, or from Silver level to Gold level.

RtL pg 24
Each monster has a Copper, Silver, Gold, and Diamond form. At the start of the campaign, all monsters begin in their Copper form. The overlord can upgrade all of the monsters in one category (humanoid, beast, or eldritch) by spending the XP shown on his Avatar sheet, according to the following rules.
• In a Copper level campaign, the overlord can only upgrade one monster category to Silver form. (He can’t have any Gold-form or Diamond-form form categories.)
• In a Silver level campaign, the overlord can have any number of Silver-form monster categories, but only one Gold-form monster category. (He can’t have any Diamond form categories.)
• In a Gold level campaign, the overlord can have any number of Silver-form and Gold-form monster categories, but only one Diamond-form monster