I remember reading something that indicated that the Goldring is NOT a Rega P2 clone--the design is similar, but not the same. This would help explain why it's cheaper than the P2 or the NAD. Presumably, it won't perform as well, although, given the good press, it should be a good turntable for the price.
As far as I know, the NAD is very similar to the Rega. (But don't quote me on this!) The one difference I know of is that the platter was different in the early years, although I think Rega started using the NAD-style platter later on.