Cat is peeing blood after antibiotics for UTI?

We took my male cat, 3 years old, to the vet on Wednesday, so 3 days ago, because we thought he had a UTI as he was peeing in the dining room, when he's an outside cat. They kept him overnight because he didn't pee at all when they had him. He finally peed and they found crystals in his urine. They treated him with an antibiotic shot that should last for 2 weeks. Our vet informed us of obstruction in male cats and that we should get him a litter box to keep track of his urine. They also gave us prescription wet food, I think it's to take care of the crystals in his bladder? Anyways, he didn't want to eat the food and if he did, it was small amounts of it. He only peed small amounts in the litter box and he would squat there as if he was peeing a good amount. Today, I looked after I saw him use it, and noticed that there was blood in the small amounts he was leaving. He's currently sitting at the water bowl and has been drinking from it for the past 5 minutes. I'm wondering if this is turning into obstruction and if I should take him to an overnight vet. The thing is, it's my parents who are paying for this and my mom doesn't want to take him to a 24/7 vet clinic because they charge ridiculous amounts of money.

Do you think he is just getting over the UTI or there is something more serious here? I'm worried he may die because I know that it can happen within as little as 24 hours.

Another question, how much does it cost to have him unobstructed, if it does happen?