I found an object with a metal detector that looks like a meteorite but is non magnetic. What are the chances?

It's almost impossible to say without a detailed study, but my gut feeling is that meteorites are pretty rare and most likely you have found a nugget of non-meteoritic material. Usually iron and nickel go together in meteorites. Have a look at the article in Astronomy May, 1997 P. 88 for pictures of meteorites as a reference.