Injection moulding is cheaper than you imagine now. The cheapest moulds start from about $250, and there are plenty of companies who will make a mould and make and ship 5k parts within 7 days.

These designs would need quite a few changes to be injection moulding compatible - for one thing the fins are probably going to have to be flat not circular due to draft angle requirements.

Changing the core to a roll of embossed steel foil might be a better bet, and whilst that would add about $1 to the price, it would also make the product work better and be more compact or more efficient due to a higher thermal mass in the core.