Replacing outside AC unit or the AC entire system?

[Haiyang A.]

The condenser in my outside AC unit was stolen (there is literally nothing inside the case). An HVAC person says that since my AC system was on R22 and shows it's age (outside unit was pretty rusty), he recommends replacing the whole system -- new outside unit, new lines, and new air handler. I am sure that the new refrigerant type (R410?) and system would be more efficient, but it will cost quite a bit more. Do I truly need to replace the whole system, given that the inside coil and blower fan, in my view, doesn’t look too bad? And input on this would be appreciated!