A natural result of low refrigerant is icing in the evaporator, it is not caused by it leaking refrigerant directly. Not moving the right amount of air over the coils can result in some, too, but that is not his problem.
I had my compressor replaced last year...did not replace the evaporator coils or lines, the old one was a 14 SEER, replaced with a similar unit - cost me around $4k. Depending on where you live, and what you have, labor rates and the price of the unit will differ, higher or lower. Our labor rates are above average, but not at the top tier as seen in some places.