Hallo, wonder if anyone can help.

I have a 1998 160 Elegance and the ignition started playing up ages ago, just on the odd occasion. Very suddenly, Friday in fact, it's almost impossible to start:

I unlock the car, put the key in and then turn as normal. It either catches 1st time or is as a dead as a dodo apart from the SRS light on the instrument board.

Sometimes after a while, all the lights come on and if the keys not too far turned, you can switch it on, otherwise, it's back to square 1.

I'm fairly certain its the ignition switch but:

Wonder if it's a common problem for A classes
What the unit looks like (a whole steering column or smaller unit)
How easy is the old one to get to
How much it's likely to cost not using mercedes?

Thanks