[shipwright]

It may be doable, a budget setup would be two half-duplex SDRs (synced with the same clock source between them), paired with diametrically opposed end-fire radiation pattern antennas in which one transceiver acts as Tx sends step-frequency continuous waveforms into the field and Rx collects the reflected signals, baring the snow the surroundings should be homogenous enough to pick up the wallet hopefully! Initially thought of a different approach than bouncing sfcw as well, but suggesting this because it has a properly documented success after a quick search: http://pe.org.pl/articles/2019/9/7.pdf

Best of luck :)