You are looking at considerably less than $1000 in parts cost for this work ASSUMING it needs it. These are common things that need attention on a 300E meaning two things; it means that it is plausible that it needs this work but it also means that a tech maybe making a quick diagnosis with the common items because they're common.

If you're not one for using wrenches find a good independent shop that does MB work and get a second opinion and a second estimate. Those prices are high even for a dealer. If a doctor told you that you neede a lobotomy, I'm sure you would get a second opinion. No different here.

Good luck,