Hi Danny,
I can't comment directly on the camera you mentioned, as I have only ever owned canon's in the past.
As Spud has mentioned, the D3100 is a plastic bodied camera, it is light, and quite compact for an SLR.
Would you consider buying used? You'd be able to pick up an older metal bodied camera within budget. (I recently sold a Canon 40D for £290 ish, which was mint, a 50mm F1.8 for £60, a 55-250IS lens for £130 or so).
What will you be using it for? I'm assuming you might try and take photo's of RC cars? If so, you'll need a decent lens or two.
Take a look at
www.talkphotography.co.uk Its an excellent forum, with a classifieds area.