Any repair shop with an SDS can test your key. Hopefully, you can find a competent independant shop close to where you live. I know from the last thread you started that you're two hundred miles away from the nearest dealer, but it doesn't look like you've got much choice.

Let me offer some advice concerning your situation. Order a new key. I know you don't want to spend the money, but like I said in the last thread, anybody who owns a 98' or later MB and only has one key is asking for a headache. I think you're finding that out now. If you get a new key and the problem isn't fixed it's not the end of the world. You can proceed to have the car fixed and you'll have a working back-up key as well as a new one.

For what it's worth, I see clients' go through the same thing as you're going through all the time. It's always the same story in the end. Most of the time the issue is resolved by replacing the key. In some cases the EIS (electronic ignition switch) needs to be replaced. Either way, you can't enjoy your car if you can't drive it. Let us know how it goes.