I am not familliar with MB a/c systems, but I am VERY good with a/c in general.

You need to find out if it has any refrigerant left. If it does, your a/c is sound and you have a mechanical or electrical problem that needs to be sorted out. Given the age of the car, chances are it is empty.

First, you need to find out where the a/c went. You would just be wasting your time having it recharged. If no leaks are found, make sure the system is dyed with UV tracer dye. If it leaks out, it can be pinpointed with a uv light.

Second, if the unit has a drier, have it replaced. Make sure this it done only after the leak has been found. Being open to the atmosphere will have saturated it. The only time I wouldn't replace it is if it causes more damage replacing by breaking off lines etc. If it comes out well, replace it.

Do not use the off the shelf fix you a/c in a can crap. Leak stop is only for selling the car. Fix it properly. Don't let anyone talk you into using that junk. Also, don't use the "replacement" a/c in a can refrigerant. It is just refrigerant grade propane. Some states ban the use of it in automobiles do to the potential fire hazzard if you are in a crash. It is otherwise safe to use. You can smoke away without fear. A/c leaks are usually so small, you would not even be able to set the leak on fire. The propane is also molecularly smaller than the microscopic pores in the rubber hoses. It will leak out.

Depending on the availability of R12 (the old bad for the ozone stuff) in your area, you may consider converting to R134A (the new not so bad for the ozone but bad for the mechanic stuff). I have done this. All that is required is to remove the R12 oil from the lines ar add a converting oil, and recharge with 60% of the rated R12 capacity. You don't need to change seals, compressor, lines, etc. It will work just fine.

How much this is going to cost depends on what parts (if any) are needed. A/C lines can be made and it is generaly cheaper than buying premade ones. Get them out in one piece and take them to a hydraulic hose specialist. Most do A/C lines as well. They can make them up while you wait.

Make sure the person you are having do the work knows what they are doing. If they try to use the crap in a can, walk away. No, drive away.