Best budget landscape manual lens for FF?

Hello,

I have a 5D mark I and use a 28-105mm II f/3.5-4.5 as my walkaround lens. I also have a 50mm f/1.4, 85mm f/1.8 and 70-300mm f/3.5-5.6. I'm very happy with my entire kit, with the 28-105mm II far exceeding my expectations for 95% of what I need it for. The only major 'gap' in my arsenal is a high quality wide-angle, landscape shot, with which the 28-105mm is just OK on Full frame. I used to have the 28-75MM tamron and that was better than the 28-105mm with landscapes, but very slow focusing and limited range kept it from being my 'walkaround'.....

is there a decent 24mm or 28mm manual prime out there that I could use just for landscapes that won't break the bank? I would only use it for landscape shots, etc so I think i'd be find with partial, if not full manual.....

Thanks.