Hiring a mage to identify a magic item is effectively commissioning custom magic research. This would be handled as per the rules in ACKS, Chapter 10, Buying and Selling Magic Items, sub-section Commissioning Magic Items:
"The adventurer commissioning the item will be responsible up front for paying the base cost and the cost of any precious materials, and for providing any required special components. If the spellcaster successfully completes the item, the adventurer will then be charged an additional fee equal to 7,000gp per month, or twice the base cost, whichever is greater."
The fee of 7,000gp per month probably seems anomalous. It's the monthly cost to hire a 9th level character.
Since researching an item takes 1,000gp and 2 weeks (1/2 month) base, and requires no special components or precious materials, the cost would be (1,000gp) + (7,000gp/2) = 4,500gp.
Yes, I realize this is incredibly expensive. It's meant to be - the "magic item market" is intended to be very inefficient. It can cost as much to identify an item as it costs to make an item. As a result, many items are left unidentified, or only loosely IDed via trial and error.
Keep in mind that you, as Judge, control the extent to which an item has to be identified. For example, in the Auran Empire setting:
- Most wands and staffs bear runes that indicate that their command word
- Most potions have distinctive smells and textures that hint at their effects