Hello- I don't know where you got that $3000 price. I just had a Espar Airtronic 2 heater installed in my Sprinter 3 days ago, and it is $1400 installed with a 2 year warranty. It works great. Call Ray at Espar of Michigan, 9675 Harrison Rd, Suite 102, Romulus, MI 734-947-0123.
If that's still too much $$$ you can keep warm while sleeping with a bunk heater, for sale at truckstops for $40. It's just a heated mattress pad that plugs into your cigarette lighter socket. Mine keeps me warm down to 20 degrees. In a cargo van like your Sprinter you must have the bunk heater plugged into an auxilliary battery because if you have it plugged into the battery under the hood your Sprinter won't start in the morning. (Yes, I did that once.)
Vipra