HVAC repair or replace entire unit?

Our house is 9yr old and we moved into it last yr. Have a Rheem 2.5ton, 10 seer HVAC unit, Model no: RAMB 030JBZ. It is not blowing cold air and the technician mentioned that the evaporator coils have a leak and is quoting $1200 to replace them. He showed me the evaporator coil and it is clearly corroded and leaks the liquid. A new unit would cost $5000. What is the best option now? Do these units run well if we replace the evaporator coil or could they run into other problems considering it is 9 yrs old? What is the average life of these models ? Thank You!