A museum quality artifact like that is priceless. Very few survived and most of them were huge and collapsed with the building they rested on. If I had a full sized complete Cretan fresco I wouldn't sell it for less then $50,000. But maybe as low as $5,000 if it's a small or fragmented peace. It's really impossible to tell without seeing it for myself
The value of an original 1600 BC Fresco from Crete could be anything between $255.16 and $350.00. The exact cost will depend on its physical condition. You could take the painting to an arts antiques shop and get it appraised.