That's a very reasonable price from VW. I would guess that the Mercedes would use the exact same 32.5% urea solution.
The Touareg holds about 4.5 gallons of solution and that'll last the average driver nearly a year. I'd probably spend more money on windshield washer solution than I would AdBlue.
This whole diesel treatment chemistry is very fascinating to me. My Jetta doesn't require a additive but I wonder if possibly 10 years from now will I receive a anonymous package from UPS containing 10 years worth of diesel soot that has been mysteriously stored for me someplace in area 51, Nevada.
I think VW, MB and BMW all are the 32.5% UREA solution. It seems like that's the industry standard, thankfully.
Pilot Travel Centers are starting to install AdBlue pumps for the newest big-rigs which have SCR systems. I haven't seen pricing yet though. Looks like they will also sell individual bottles too! My guess is that will be cheaper than any dealer would ever be.
In bulk quantities, urea ought to sell for around $1/gallon. So any price greater than that for windshield washer fluid is too much.
Question: if urea freezes, is it still okay to use after it thaws out?
I've been looking a lot online on urea/AdBlue and from what I've read it's perfectly fine to use after it's thawed. Apparently the Urea has a shelf life though of a year or two, then it's "bad".
It seems that the MB and BMW diesels (at least) with the system have a holding tank heater. The car runs without injecting the AdBlue intially (since it's frozen) then it will squirt as it begins to melt.