I've never seen an MCU replacement come with a core charge associated. If they want to charge a core charge, they can, though I'd expect the MCU price to be reduced significantly to account for it... It also needs to be specifically called out as a core charge. They can't just charge you to keep what belongs to you because they feel like it, especially so when charging you full price for the replacement. (To be clear, your current MCU belongs to you. You are buying a new one from them for $XXXX. Both belong to you. This is different than agreeing to give them your old MCU in exchange for a new one for $XXXX-$YYY core charge.)