Bone Cancer In Dogs

my dog was recently diagnosed with bone cancer(sniffle)…he was prescribed rimadyl (an anti-inflamatory)…hes been hangn’ in there for about 2 months now, the script is really starting to add up. and being that its simply an anti-inflamatory im wondering if i can substitute it for something over the counter such as advil, tylenol etc….now, im well aware that a vet would never condone this, but im wondering if its a possibility never the less and if so what would be equivalent to 100 mgs of rimadyl?…please, i love my dog very much. and id never sell him short, so im not interested in opinions or speculation… strictly hard facts. your sensitivity and accuracy will be greatly appreciated….also, is there something stronger out there that i can give him(not pain killers)?