Glad the info from me has been useful.
Its hard to keep costs down if you need 24-105 'L' performance (~$1700 new) and WR.
The DA18-55WR; DA50-200WR and 18-135WR are pretty good in performance and have WR at very low prices. (as quoted above)
They can even be as sharp if not sharper in the center than the 24-105L, but the latter does have more even sharpness over the whole frame and is F4.
The high end of the Pentax zoom range to meet your requirements would be a DA*16-50/2.8 and DA*50-135 (~$1K each 2nd hand; ~$1350 new).
Both are weather sealed lenses and optically very good, but these are 2 lenses, not one, and covering UWA 16mm to short tele 135mm at f2.8.
Perhaps these 2 lenses will suffice all you needs from vast landscapes and grand buildings to longer reach use and portraits. Low light usage too given their f2.8 aperture.
So its an alternative to 10-22; 24-105; 50/1.8 (the 10-22 is not cheap either).
Win some, lose some, no perfect solution
My suggestion if I were you:
a. K5; bite the bullet and get the 16-50 perhaps plan for a 50-135 later or just get a cheap 50-200WR
b. K5; just the 18-135WR and get other lenses as you learn more of its strengths and weakness
c. K5; 18-55WR and decide on other lenses later.
DA18-135 isn't too bad a lens.
I did a review of it a while ago.
http://www.clubsnap.com/forums/pent...ax-da-18-135mm-f3-5-5-6-ed-al-[if]-dc-wr.html
Look at the other suggestions too. That suggestion of an old 5D+17-40 is viable as well.