I would start by not using a tech that tells you what his guess is. Find someone that will actually take the time to find the problem and explain your options.
Agreed! You need to find a real service company. I wonder if they can fix what they install.
The overall picture of the system's condition should have been taken care of the first visit, including determining the state of refrigerant charge, and location of the refrigerant leak. The components do not have to be isolated as stated in an earlier post to perform a basic initial leak search.
There are many ways to skin a cat for the improvement. A good company will explore and present all options, qualify your specific needs, and provide the pros and cons for each choice. Whether you maintain an R-22 based system with piecemealed components, replace system with basic efficiency, or replace everything with a high-efficiency 2 speed R-410A system your choice should be made after a thorough assessment from a qualified professional. While your budget is a factor, there is a lot more to consider here than just your initial cost. Comfort, operation efficiency, indoor air quality, and independant humidity control are all factors that should drive your decision.