This is a common issue that arises with cats (urinating in the sink etc) but unfortunately the treatment is not an easy one. It sounds like either a urinary tract infection or something more serious (due to the weight loss and depressed attitude). I believe the skin lesions are not related.
Unfortunately there is little that can be done to help without a vet's visit. They will need to examine your cat, assess the urine and prescribe medication. There is also a concern that this is related to kidney disease, a kidney infection, urinary stones etc. and all of those are urgent in requiring treatment. Here in Canada there are great third party financing companies (petcard is one of them...maybe theyre in the US too) that can help with delayed payments. I hope you can understand a vet's reluctance to create their own payment plan options.
I would also have a feline leukemia test done. The symptoms really sound familiar, I had two cats years ago who has this disease. I hope that's not what it is.
Hey Rssa, your problem s :unds familar to one I had with my oldest cat about 13 years ago.... same thing bumps under neck, hairless butt took her to vet she had allergy to fleas . They gave her allergy shot (steroids) and within a day or two all better ( hair took a while to grow back) . I never seen a flea on her neither! i still have to take her about 2x year now for same problem. Total cost around 40.00 . Hope this helps ; )