Tonight I cashed in all of the Magic Items placed at the Academy and tallied the individual and total amounts awarded.
There are 25 total. We have 24, the only missing item is the Volcanic Vault. The Vault is listed as a non money item in the Strategy Guide so the financial estimate should be accurate.
Bottom Line: Each item gives @150 gold pieces. There is some slight give and take but $150 each is a good average.
So I activated all 24 and got Two magic items instead of cash.
I don't know if this will change over time or with experience gained like a rising Portal Master rank but that is what it was today.