Just so you know my cat sometimes poos/wees blood and have taken him to the vet many times, and never can say whats wrong with him!
It will go on for about a week, then will stop. They always just give him some anti-biotics, but then he's fine.
They normally charge about �35 for vets time and pills. He is 18 now and still going strong.
The vet normally says to us if he is off his food then thats when know something is wrong.
If he isn't in pain then can't imagine they would just put him down, perhaps try course on anti-biotics first.
Is he still eating?