Nick - Noone here is trying to discourage you from working on your own a/c system. The message is more along the lines of "learn first, dive in second." A/C is not a learn as you go kind of proposition.

That said, getting a handle on the basics is not that difficult. Haynes publishes a generic automotive a/c manual that will get you started. It contains a good overview of the theory and practice, lots of service and troubleshooting tips, etc. About 10 bucks.

You'll need specialized tools to diagnose & service the system - a set of guages/hoses, can taps, and a thermometer at a minimum. These can be chased down for about $100. If disassembling the system, it needs to be evacuated before charging - a vacuum pump is a necessity. You'll need to budget $200-$300 for one, unless you can scare up a good used unit. An air compressor is also necessary if the system needs to be flushed - though a very small unit will suffice for this task.

So depending on the complexity/severity of the problem, the tools may cost more than simply paying for one repair. If you don't like the MB dealer, perhaps there is a competent shop which specializes in a/c?