I have the following setup and I am pretty happy with it.
1-DA 16-45mm, it's for sake of the APS-C crop factor. A must, IMO IQwise not much different than 16-50mm other than extra 1.5 stops, lighter, cheaper. This is my only DA investment, because I am a future FF believer. (new $350)
2-FA 35-80 mm very good lens (used $40)
3-FA 100-300mm this is the incredible star lens among the herd, strongly recommended, Ill post samples if you want to.. (used $100)
4-For the sake of the 1:2 macro Tamron 70-300 LD-Di (new $250), not needed much.
Total of $740, without not so necessary Tamron it's $490, god bless Pentax)
Also, I've just tried my wife's Pentax DA 18-250mm, only yesterday, just arrived, it's a mediocre lens, IQwise I can't recommend to anyone except who insists on a wide range walk around lens, or to someone like lens changing hater & having a hard time in transition from ZLR, just like my master.