Need to bring dog to veterinarian ASAP this morning

Our 15 yr old dog suddenly lost his ability to stand up 9pm last night. We dont really have a lot of money to go to the animal hospital, we will do it last resort but I wonder if anyone here knows of a vet open today, Saturday, where we can walk-in or book a "sudden" appointment this morning? Any advice will be greatly appreciated. I'm Houston Heights area.