I had the same requirement and here is what I did:
click for link
I really wanted a water cooled 1800 RPM unit, but couldn't see the additional cost. I actually "shopped" for over a year. These units are $ 4000 on up, unless you are willing to buy a high-hour mil surplus unit. My interest was in something fairly new and reliable, with easy to find parts if required. I ended up buying an air cooled 3600 RPM unit. It is a step down in life and noise, but I rationalized that since it is 100' from the house in the shed, noise was not a driving issue, and since it was for backup duty, life of an aircooled unit would suffice. I compromised on my goals, but I am quite satisfied with what I have.
Last week we had a power outage at 10:00 PM on Friday. It was 5 deg out. I waited a bit to make sure that it was not a short outage. I hopped in the car to take a look-see, since the substation is only a few miles away, faults are usually local. Sure enough an SUV plowed through a pole and into a house. Wires alll over the ground. I cranked up the genset (two quick shots of ether were needed due to the cold temps. The house had lost 4-5 deg in the 30 minutes of outage. I ran my 3 heat pumps as well as normal lighting, TV, computers, etc. The power was out 8 hours and we kept nice an warm, as the temp dropped to -5 deg that night. I'm sure some of the neighbors were not as comfortable. I was very pleased to see that I only consumed 3 gallons of diesel over 8 hours, with about my worst case load.
It's too bad you didn't post a week or 2 ago. A guy at work just sold a 15KW unit with a Kubota engine (3600 RPM however), in a doghouse and integral tank and control panel, for $ 2000. Very low hours as well. I almost bought it, but I felt what I had was sufficient for my needs, and it would need to sit outside, a negative wife factor.
You might want to check with these guys:
http://www.centralmainediesel.com/order/ES12000D.asp?page=ES12000D
They have a good selection at what is reasonable prices. I linked one particular model, but they have a wide range available. I also found that in general, eBay rarely has good deals for "nice" units. Also based on many examples I have read stay far away from the Chinese imports. For example:
http://gpsinformation.net/chinagen.htm
Gool luck in your hunt.
paul
EDIT: I shortened the text for the link.
