About how much will it cost for a consultation involving cat diahrrea?

My sister found a stray kitten about 1-2 months old. She had a cold but we where able to help her with it. However a week ago the cat showed signs of blood in her feces. We did not take her to the vet but we started giving her intensive care. The cat shows no signs of being in pain right now. In fact she is playing and running around like a normal kitten. Now her feces has no blood but its still almost liquid. Should I be concerned and take her to the vet? If yes how much will it cost?