Hi, Kid, and welcome to the forum.
I have an E320, the oil change procedure is virtually identical and there's a DIY post with pictures for it here: http://forums.benzworld.org/gallery/...ial_Oil_Change
It's not particularly challenging to do yourself, just pay attention and you should be fine. Three caveats, all of which are mentioned in the DIY: be sure to buy the proper filter assembly wrench for your engine, be sure to get the fleece oil filter kit, and be sure to get Mobil1 0W-40. So far it's the only one I've found with a label that specifies it as meeting MBZ spec 229.5.
You'll need to buy 9 quarts of oil, about $6 most places, plus the fleece filter is about $14 on line, so it's roughly $70 for the oil change. Most dealers around here do them for about $95. I'd guess the $350 quote is for a B service, which includes the oil change.
Lots of the folks are fans of using a suction pump rather than using the drain plug, I think it's largely a matter of preference.
If you don't want to DIY, call around to dealers and indies and ask for pricing just for an oil and filter change. Just don't take it to a jiffy lube or some dump like that, they probably won't have the correct oil or filter and you won't save any money there anyway.
Take care and enjoy the ride,