For that amount of money you could replace the coil, condenser, and line set.

How much refrigerant was added and when was the last time the charge was checked? What temperature were you trying to achieve? It hit zero degrees yesterday in NJ which is unusually cold. The temperature is expected to drop in the single digits on Tuesday night. Your heat pump is not going to be able to produce enough heat at these temperatures.

Do you electric heat strips for back up? Do you know how the size of the heat strips?

That estimate to fix a leak is outrageous. This is typically done to convince you to replace the system rather than repair it. Unfortunately most HVAC companies operate in the same way. Get several estimates on a leak repair (you may have to pay the first company $100-$200 for the leak test) and, separately, get several estimates on replacing the system.