Ebay offers Apple Memory Module 16GB DDR4 2400MHz SO-DIMM 2x8GB - MP7M2G/A for $76.50 (reg. $125.84) after code free shipping.

Apply Code: RETAILKING10OFF

Product Description:
• 16GB DDR4 2400MHz
• 2x8GB
• SO-DIMM
• Compatible with 27-inch iMac (mid 2017).
• Apple Memory Module 16GB DDR4 2400MHz SO-DIMM 2x8GB - MP7M2G/A