Here's the link link to tell the real ones apart from the repro -
http://www.imperialgunnery.com/vehiclesplaysetsother.htm
The one problem with this link is that the ones Iain sells (itfciain), look closer to the originals as they have no circle around the peg. I have some originals and they do feel different in hand than Iain's ( slightly heavier) and also have a slight texture to them on the bottom when held up at a certain angle in strong light. Another thing is that Iain's have two half circles on the underside ridge that I don't think are present on the originals (been a while since I looked at mine though). Quite difficult to tell from a picture and as mentioned in the TIG link it might be easier to find ones that came with action force.
The price feels about the going rate and these are normally missing from the Palitoy Death Star play set hence the price. As I side note I seem to remember 5 of these coming with the play set but it could have been more.
Ian