How mechanically inclined are you? If you know your way around a wrench, have installed an aftermarket radio and feel comfortable ripping apart your dash, you can save the $100 bucks and burn up an afternoon getting to learn what's between you and the firewall. I've done audio installs for years and would rate this an 8 out of 10 with 1 being easy and 10 being damn near impossible. Reason I say this is because you're really supposed to drop the steering column to get it out, and with that being said, it's a long ordeal. It can be had out without but you run the risk of cracking the clear part and dealers know better when you tell them it just cracked and they begine to ask a lot of questions, don't ask. LOL You can find the procedure in the SRT6 service manual thread. It's the same for '04-'06 and the '07-'08 has an airbag you need to disconnect before you start any work so make sure you disconnect the battery before you start working and let the car sit for a half hour before tearing into it to be safe. PM me if you need my number. I've had mine apart 2-3 times so if you need help with something that the manual doesn't clearly explain, I'll do my best to get you out of the dark and on your way.

Also, the SLK320 cluster will work if you have a base/limited but you'll need to switch out the face plate portion and put it into the original one so you have the correct mileage. AMG will not work on the SRT6 or base/limited as the numbers go up to 180 instead of 160 or 200.

Hope this helps.