For all you depth junkies:
Some people only ask one question; "How deep will it go?" Depth is FAR from being all-important! The whole "My detector air tests six inches deeper than yours, Nannernannerbooboo!" only shows a pronounced lack of knowledge about metal detecting. Up to about six or eight inches in depth, digging holes is not a big deal. If you are in rugged ground, and your detector can reach three feet on a big gold nugget, identification becomes just as important as depth. That was a big problem with Pulse Induction Detectors originally. With no way to discriminate between low conductive gold and highly conductive iron (or hot rocks), people were digging two or three feet into hard rocky ground just to find a nail or piece of barbed wire. Anybody that has ever had to dig those kinds of targets several times a day can tell you that identification becomes just as important as depth.
Anybody wondering why detectors are so expensive now is not knowledgeable about all the research and development that goes on in the detector manufacturing companies. Their electrical engineers are constantly traveling to test theories about depth and ID. Western Australia has some of the worst ground for metal detecting in the world. It is unfortunate that Western Australia also has a crap ton of gold still in the ground. Its no good to have a metal detector that will reach five feet deep on a target, but can't give you any idea of what that target is. One way would be to carry something like a Fisher FX-3. A very basic magnetometer. It will reach up to about fifteen feet deep on a large target (car size). It only sees ferrous targets (iron, steel, etc). So, if your detector finds a deep target, then waive your magnetometer over it. If it sounds off, that means your target is not gold, and you can ignore it. BUT WAIT! Maybe that piece of old saw blade is sitting on top of a two ounce nugget! THAT is when you need the Holy Grail of metal detectors: One that can get REAL depth, AND identify what it found. Every electrical engineer at every detector manufacturer is looking for that same thing. A balance between "How deep can it go?" and "What will I find when I dig it?" The kind of knowledge and experience that it takes to overcome problems like that doesn't come easy or cheap.
Mike