Cave/void detecting-I need solution for up to 500euro...

[Flareproof]

Hi I'm new to here, so basically I run with my garrett250 on weekly basis but for some time now I'm more and more into caves detecting, I've done some research but can't decide which way should I go. I found echo sound method quite cheap but is it reliable?

[Funfinder]

500 Euro? You can try to find some older secondhand JeoSonar from Turkey which detects cavity.

Or you look for a non-motion circuit detector with large coil and manual ground-balance,
listen to the threshold-signal and when it starts to get silent there might be some cavity.

But the best detectors for cavities are GPRs - 3000 Euros upwards!

However - you only will be able to detect cavity if the ground is medium-mineralized
so some contrast is recognizable - as long as the cavity is not too deep below the surface.