Subby's the man over at the SLK bbs.
He's running his roots blower up from the stock 0.5bar to 1bar through a port and polish of this SC and machined smaller pulley.
Here's a link to his full thread.
On page 2 it mentions $80...but that's a couple of years ago.
Intercooler Spray testing.... - Page 2 - Benzworld.org - Mercedes-Benz Discussion Forum
It uses the window wash water bottle (about 6-6.5L/Qrts) as the reservoir which laos has your stock indicator light to tell you when it's nearing empty.

It would be much like the evaporative coolers you see in the ceilings of shops etc. in inland areas.
The evaporation of water (2,252kJ/kg) takes 8 times the energy away than it takes to heat water from 86F(30C) to 212F(100C) (300kJ/kg) or for that matter the energy required to melt ice (334kJ/kg)
Now since our HX (behind bumper) shouldnt get above 140F(60C), you wont be boiling water on it, but that is also the case for the A/A coolers used in the high boost SLK230's which get to maybe 180F(82C) at the HX inlet. The water mist still evaporates, taking the heat away with it.

An example calc would be - if you're under race conditions, and it takes you half an hour to use the 6L of water - wack in a drip/waste factor of say 50% and that's about 3.8kW (12,500BTU's) of additional cooling (or about 18F(10C) drop in IAT at WOT)
Putting that into context - it's just south of what a supercooler upgrade is worth for heat rejection.