You can't just buy the motors I am afraid :
You have to buy the complete mechanisms. I have just had to change a pair in my 1987 190E cossie. They are quick to change but they are expensive to buy new. Something like £130 each side if I remember correctly (from the stealership). I found that it was the motor that had gone in both cases, and was going to get the motor reconditioned. In the end I picked up a set of 4 doors for a ridiculous price and had the mechanisms out of that!
German and Swedish sell patterm part mechanisms for about £60 each but I looked at them and they are crap!
Stick with originals if you can!
See if any places in Ireland will recondition the motors for you - I was told of a place near me but got the other doors first!
Or keep an eye on ebay. If they are just stuck down you are in no real rush, some are bound to turn up soon!