Macro lens for Nikon D3100? - 2

I'm looking to buy a macro lens for my Nikon D3100 camera and the maximum I want to spend is £100, I know I won't get a nikkor lens for that but can anyon le give me any suggestions for this price range thanks

You need a 50mm prime lens ( with diaphragm gear ) and some extension tubes

A 50mm lens and some close up lenses (+1,+2. & +3) from Tiffen is what I would use if I had to be that conservative with the bucks!