I have been adding a can of 134a with leak fixer and or oil. Whatever is on sale. Which is usually the leak seal crap. I didnt think about it but i bet i have about 4 or 5 cans in that system.
I wish i could do my own work but i dont know much about a/c. I can rebuild a trans, setup a rearend or build an engine but i have stayed away from a/c work.
It can be done at home. You can pick up a used manifold gauge set for around $50 if you look around (heck I've seen new ones for that). The vacuum pump can be bought for $100 as well..or less if you get a pneumatic one, but be prepared...the pneumatic pumps need a GOOD compressor (lots of CFM). Or build one out of an old junkyard refrigerator compressor. Info for that is all over the 'net.
Vacuuming the system is probably the 2nd most important part. What you're doing is removing the moisture. Water boils at 212 deg at seal level, which is somewhere around 14.5 psi actual pressure. We don't notice it because we're used to it. If you pull the system into a vacuum of around 29" of mercury, water will BOIL at around 50 degrees F if memory serves me correctly (chart not in front of me). When it boils, it is removed from the system and therefore the system will work as it's designed to. Moisture in the system will cause compressor to work harder, also causes corrosion and reduced cooling ultimately.
Need to get all the original stuff out. Usually flushing is best. The flush stuff can be bought at the parts stores. You'll also want a new accumulator for sure. Usually comes as part of the hose assembly. If the condensor is dinged up, it's cheap to replace as well. Usually around $100 give or take new. Most expensive part is the compressor. Good to replace it. But as long as there's no metal in the system it might be salvageable.
You'll want to have the system recovered. Most places don't charge much for it. They're just removing the 134a that's in it. It can be done at home as well but how you go about doing it is your business. From there, just as matter of replacing defective or broken parts. Then flush. Then vacuum to check for leaks. Then add oil to the system once it's leak proof. Then start the engine, put some heat in it and then vacuum it down one last time before adding refrigerant.
A/C work at a repair shop is expensive. Why? Lots of overhead. Tools especially. Recovery units are $2500-$10,000 depending on what kind they are and what they do. Every A/C repair has a little bit of $$$ built into it to help pay for the tools. Then labor. If a tech has to replace an evaporator it's not cheap (long job). If you have the time and a couple of the main tools, it can be done in your garage for 1/10 of what a shop charges. Fixed my '93 LX 4 years ago (was originally R12, o-ring failed & leaked it out)...R&R'd the accumulator, o-rings, flushed it all out, replaced compressor with a JY unit and recharged for around $100 total. Labor was free because I did it. I did buy the gauge set and vacuum pump though and that was a chunk of change but I use it at work too (tractors) so it's more or less paid for. I still need to buy/make some sort of recovery unit...but most of the stuff I've worked with has already leaked the refrigerant out totally and those that haven't are repairable without opening the system...so far. Had 2 or 3 that needed recovered but we had a mobile a/c repair guy do that for free. We just let him have the refrigerant. If it's R12, they'll pay us for it.