We have been developing a low cost magnetometer for archaeology surveying. Our first twin sensor gradiometer prototype has shown promising results but is not as sensitive (>3nT) as required for good surveys on low occupation sites.
A four sensor prototype is being constructed that, along with improved microcontroller processing, should allow sensitivities in the range 0.2-0.4 nT.
Field Testing will commence in mid 2017. The target price for the production units will be <£1500.