It's really hard to say how long the HF bio-cleaner I currently use will last, because the design of their parts washer has the solvent permanently sitting unfiltered in sediment and oily goo that's constantly stirred up each time the pump runs. With the separate tank and filtration setup, I should be able to extend the lifespan of any solvent I use, assuming it doesn't go rancid. I think B100 runs around $3.40/gal, while the HF stuff is closer to $4/gal. I recently ran a gallon of B100 that had been sitting for ~6months in my little tractor and it purred just fine...of course, I also mixed it with some used pre-filtered ATF as well, so that purring may have had some contributing factors