Why not consider the Pentax 12-24mm used fits nicely into your budget and is wide enough for most architecture. I have and like the Sigma 10-20mm f3.5, which is also in your price range and goes wider but not as long. I would pick your wideangle zoom based on the lowest distortion, unless you love to process and correct it. Prime or zoom of 50mm plus would make a nice and small addition. Might be a good time to take the relatively light and small 100mm macro with for close-ups, portraits, and architectural details. Use it before you sell it, in addition or in place of a 50mm...
Last edited by mtgmansf; 11-10-2018 at 04:03 PM.