You can create simpler versions with home appliances. Metal detectors with metal detector, in this instructional video, you'll see how to create a metal detector of only two household items, and under twenty dollars. So, if you chase the treasure, and don't have the money yet, then make your metal detector. There have been advanced applications that allow you to use your own magnetic field phone to detect metal objects.
Professional metal detectors are simple but require a bit of work to make. But you can build a reduced portable detector using a calculator, AM/FM radio. While building a conventional metal detector may require several, you can create simpler versions with home appliances.
How to make simple metal detector at home
Find gold with a homemade detector
Radio Calculator Metal Detector