Cost to replace heater core for a Honda Prelude?

$150 for the heater core, $595 labor. (Refrigerant recovery & recharge is NOT necessary for heater core replacement.) As a permanent fix, you can also byp the heater core. You'll have no heater, but it will stop the coolant loss so you can can continue driving. A shop shouldn't charge any more than $50 to do a byp.