Actually with a camera capable of good high ISO ability like his, the low light results aren't as dependent on a superfast UWA. Any of the UWAs today will get you similar results - quite good and lots of fun but not quite up to the quality of a good prime when wide open...all are a little better stopped down.
No reason not to shop Nikon, Tamron, Tokina, and Sigma UWA options and see if you can get a good price on one. I do lots of night and low light work with my Tamron 10-24mm and have been very pleased. I have friends with both the Sigma 10-20 and the Tokina 11-16 and both are very happy as well.
Sony DSLR-A68 / Sony 18-250mm / Minolta 50mm F1.7 / Tamron 150-600mm / Minolta 300mm F4 APO
Sony A6300 / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / 10-18mm F4 / 35mm F1.8 / 16mm F2.8 / FE70-200mm F4 G OSS / FE70-300mm F4.5-5.6 G OSS / via manual adapter, lots of Pentax K mount, Konica K/AR mount, and Leica M mount manual lenses