Unless your company is paying for it, or it's otherwise tax-deductible, don't lease. You're essentially signing a long-term rental contract when you do that.
If you really want a Mercedes, then set yourself about a $20,000 maximum budget, and go to one of the internet car search engines and see what's available on the used market. You should be able to find a four-to-five year old C-Class or a six-seven year old CLK or E-Class. Get it checked out by a good independent mechanic who specializes in German metal, and don't sign anything more than a four-year note for it.
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