Originally posted by BROO You might have to settle for a manual focus ultra wide angle lens for that price range for Full Frame camera.
11mm f4.0 Irix
12mm f2.8 Laowa
14mm F2.8 Samyang
15mm F2.4 Irix
17mm F3.5 Tokina
Just for starters
That list is valid, and all those lenses are good options.
The DFA 15-30mm is AF, WR, and extremely good. It's big though.
The DA* 11-18mm is an APS-C lens but from 14 to 18mm it works on FF. And at 11mm it works with a square crop.
The FA 20-35mm can be had used if you look close enough.
Just a note, if you want the same
field of view as what your wife gets on her APS-C camera, then 15-30 is an almost exact match. The widest mostly rectilinear lens available on FF is the Laowa 12mm.
The Laowa and Irix lenses, as well as the Pentax 15-30 and 11-18mm, have been reviewed here in-depth. You could look at the reviews to build your opinion.