I agree with Steffen. If you don't want to go to the expense of a pulse based pinpointer the Garrett is a good choice and seems to be more reliable than the Whites and many others. As for the very cheap ones that turn up on E-Bay most seem to be shocking. One I was sent to try had to be kept level after it was switched on. Just what you want when checking out the side of a hole....not !
I don't know if you have the possibility but I had them all and the best one is the Detectorpro pistol probe. I can tell you this pinpointer is a killing machine. Only problem is that it's a bit bulky.