That sucks. Especially when you can get a tyvek suit cover-all on amazon for around $25 and take that off before entering the house or at least rinse it down.

Off the top of my head I’d surmise a bad (but still way better than this) cheap way to do it would be to use one of those, a respirator with p100 cartridge ($35) and plastic tarps you use painters tape on to apply against the bottom of the wall, then collect the results by rolling the tarp up, slide contents into garbage bag and re-use tarp. Nowhere near safe (and so much dust would float beyond it but what can you do) but would cut down on soil contamination and other things. Of course if he’s fine breathing it in you could forget the respirator because he’s fine with it. But if you did it yourself that’s about what it would cost to mostly protect yourself (shaking/brushing off the suit, ideally using a garden hose to rinse it away from the house of course and then removing the suit outdoors, leaving it outdoors and then going inside to quickly shower/rinse your face). Misting anytime you’re creating or moving dust would also be advisable but may not be practical and risks creating run-off if you’re using anything but very light amounts of water (though done away from the house you’re at least removing the risk to your garden and such). Of course the proper thing to do is not this. It’s a lot more involved and expensive.