I used ATV diamond pattern chains on the rear of my BX1850. The tire size was very close and I made them fit. They worked great. I bought these chains 7 or 8 years ago from a farm supply for less than $100.
Harvey
ATV chains are certainly a cheap solution but I think they will not fit on a B7100 (mostly on rear tires) The rear tires diameter is 29 inches and front tires are 21 inches