From your description, it sounds like your cat may have a urinary infection, intestinal problem, or anal gland discomfort, due to fluid retention, impaction or infection. Scooting his butt on the floor is usual behavior when a cat has discomfort either from his anus, due to an anal gland problem, or due to an intestinal problem.
If your cat is getting hurt by other cats outside,
incurring an expense for you and endangering his own health, he really shouldn't be allowed out anymore, so he won't face any of the outdoor dangers like other animals, cars, toxic substances, mean kids/adults, which usually significantly shorten the lives of cats who are allowed outdoors.
If he sits and stares at nothing, in addition to the other symptoms you mention, this may be a symptom of pain or distress of some sort, or he may feel stressed by his discomfort causing him to
eliminate around the house. A cat appeasing pheromone called Feliway may help if he's stressed. It comes in a spray and plug-in diffuser and is available at stores like Petsmart, and also online. www.catfaeries.com/feliway.html
If your cat is not neutered, this may have something to do with his tail being straight up and quivering; but this may also be related to a urinary infection. Urinary infections in male cats must be taken care of immediately, as a urinary BLOCKAGE may occur as a result, and in male cats this is an EMERGENCY, if they can't urinate at ALL!
I realize you're a little apprehensive, because you had to pay such a high fee at the vet in the past, when he needed stitches, but your boy really should be evaluated by the vet, ASAP. I can help you find some lower-cost vets and organizations that may allow you to pay out the vet's fee in installments, at these sites:
What food does your cat eat (brand and dry or canned)? I'm assuming you checked that his food(s) are not on the recall list, which was amended again, today: www.menufoods.com/recall
It's possible that his symptoms could also be related to food allergies, or god forbid, tainted food, if his food is on the recall list. I'm sure you've checked the list, but keep checking every day, as they keep adding foods.
I hope your cat will be fine, once he's diagnosed and treated by the vet. Please let me know how he's doing and what the vet tells you. Thanks!