Since your budget is limited, I'd consider the Pentax.
You already have Pentax lenses, that saves money.
It has image stabilisation built into the body, which makes lenses cheaper than the equivalent Nikon VR lenses, because it's not in the lens. Every lens you use benefits form the vibration reduction.

The sensor seems good, I've seen some good sports images taken with it, comparable with similar price Canon/Nikon ... and Pentax have always had a good reputation for quality lenses.
Take a look at Mike's images (Didache) in the UK Members Met thread in viewfinder.