Best price I've found on Koni's for the Sprinter is at Summit Racing - $183.95 ea. for the front struts and $135.95 ea. for the rear shocks:
Koni Front Struts for Sprinter
Koni Rear Shocks for Sprinter
They show the front struts as being for the 3500 only - but the part number is the same for the 2500.
If you don't mind setting them yourself (they are already set to the lowest dampening rate from the factory - which is what Koni recommends, as even the lowest is more than the stock shocks) you can save $160 to $120 over what EuroParts or Upscale Auto charge, respectively.
Summit does not stock them - it will take them a week or two (possibly have them drop-shipped directly to you from Koni's distribution center in Kentucky) - but you do earn Summit Speed points for your purchases.
And if you have a Summit Speed (credit) Card you can possibly get 6 months same as cash (free money is always good

) on purchases over $500. Applying for the card is pretty easy - I'd imagine you can do it over the phone when you call to order - I did it in person when I went in for some stuff (I live close) and it took about 2 minutes for an approval.