Classic/Antique Car Repair: 1966 Eldorado, worst case scenario, dollar range

Question
Looking at buying a 1966 Eldorado. Heater core is disconnected so cannot test Heat or A/C. Want a range on what it would cost to replace the heating and A/C system if it came to that.
A worst case estimate would be fine.
Thanks

Answer
A worst case scenario could be as high as the 5 thousand dollar range if the heater care is bad, the compressor is bad and there are leaks throughout the system. The heater hoses disconnected tells me that there was probably;y a leak in the heater core but you do not know if the A/C was working before that. Unknown on top of unknown.