Question about Mercedes Smart Key!?

Okay so I own a 2006 C230 & I only have one key. I want to buy a spare, just in case, but the dealership quoted me $350; $216 for the key & $119 to program. But I have found some on eBay for way cheaper. My question is, can I take a key that was programmed for a different car & reprogram it to mine? And can I reprogram it myself, or do I have to take it to the dealership? Thanks!