Keep an eye on eBay, normally a few sets on there from time-to-time
Going rate is around £500 in good nick with decent tyres, a bit less if the wheels need a refurb and/or no tyres - and in perfect condition with new tyres perhaps a little more again.
I have a staggered set that's come off my CLK55. Tyres on them all but only 1 front one is of use, the rest are either near tread depth limit or worn on the shoulders. There's a little bit of bubbling near the centre hub on one of the rears. A small dark patch has appeared on the lip of one of the fronts and about an 3-4inch kerbing graze one the other front, just on the very edge of the lip.
Looking for £380 ono for them to be picked up from Manchester. Let me know if you're interested before I post them on the for sale forum.
cheers
bubbling on one rear. the vertical marks near the centre top of pic are water droplets, the pics taken just after cleaning.