As Susan said vets charge different amounts. The first vet I saw charged $52; the second one charged $42 (this was for just a normal exam). Oral Baytril was $40 for a 2 week dose from my first vet to treat bumble foot. Injected Baytril was $48, given to my chin that had a stone before surgery. I'm not sure if the price depends on how much they give you. I'd guess it does. The x-rays to look for a stone, initial $152, additional views after surgery were $55. Urinalysis was $52. I just had a recently adopted chin pass away after a surgery to have a stone removed. (I don't mean to tell you that to scare you). The total bill was over $900. I saw 2 different vets. The first vet told me it could be a UTI but they'd have to do x-rays to check. I called around and found a cheaper vet. If you call and ask they should be able to tell you the prices for initial exam, x-rays, urine test, and possibly Baytril. But, they could prescribe something different.
It may be nothing at all. Which is what I hope for you. Something in his diet could be the reason for darker colored urine. I hope your chin is ok.
They will ask you about his living conditions and diet. Has he been running on a mesh wheel? Is he housed with another chin? Could he have scratched himself on something? Done a hair ring check lately? Take a look at his feet too. I know my chin with the stone did try different corners when he was trying to pee, but I had also recently gotten him, cleaned his cage daily, and gave him bedding which he didn't have before. Any new toys in his cage, sharp corners?
Yeah, not much you can do for him tonight. Make sure he's comfortable and love him. Let us know how he does with the vet.