I'm in the Austin area, you're going to have a hard time finding someone who can a.) build an actual quality spiral straicase b.) find someone who will do it affordable. With the construction boom in Austin people who do quality work are naming their prices. If you're not as worried about price try DropHouse Design or Austin Metalworks, they do some of the best work I've seen in Austin for being big time fabricators. If they're too high for your liking get back with me and I can probably help you out or point you in the right direction.