Tokina zoom range options:
Canon 10-22mm
Sigma 8-16mm f4.6-5.6
Inexpensive manual focus primes:
Samyang fisheye projection 8mm f/3.5
Samyang 14mm f/2.8 (FF)
Samyang 16mm f/2 (APS-C only coverage)
The astrophotographers are all over the Samyangs due to their cheap cost and admirable lack of significant coma aberration wide open. Most other brand lenses are not as corrected wide open. Astrophotographers use manual focus.
Some lenses have filter threads, some don't.
I debated between the Tokina zoom, the Canon zoom, and the Sigma zoom, and gave the Sigma zoom a go. It is a fun lens with an amazing 8 mm more-or-less-rectilinear-projection wide end, with the expected barrel distortion. My copy is sharpest at 8 - 10mm, which is where I use it most of the time. Sigma at 16mm is no sharper than my (quite good) Canon 15-85mm walkaround lens. The Canon 10-22mm is highly regarded, and has filter threads, important for some people. That's my biggest problem with the Sigma - no cheap filter solution - I didn't think I would need them, but I have since discovered the joys of ND graduated filters and Big Stopper.
I also have the Samyang 14mm and have used it on both APS-C and FF, mostly for astrophotography. It is sharp in the center and meh at the extreme corners at f/2.8, and sharpens in the corner by f/5.6 or so. It is a fun lens and an amazing bargain often on sale for $300.00 USD. A relatively affordable filter system is being introduced in the EU right now, and should be sold here soon.
The Samyang 8mm fisheye is popular, but Sigma also has slightly more expensive fisheyes with different characteristics - if you don't need full sky coverage (and circular image on APS-C), the Samyang will do nicely and is cheap.
I know little about the relatively new Samyang 16mm f/2.0 with APS-C only coverage.