Get the DA55-300 plus a DA17-70 or Tamron 17-50/2.8 if you can. I prefer the colors that come from the Pentax lenses (so I bought the DA17-70 when I was in your position), but the Tamron is still very good and it's faster as well. The Tamron 28-75/2.8 is also good, but it requires you to get a wider lens like the Tamron 10-24 as well.
I liked the DA55-300, but I like my F70-210 better (actually I got the Takumar version for well under $100), so that could save you money. The DA55-300 is still better than it has any right to be as an entry level lens. But I never got an image that was
really compelling over 135mm, so I eventually sold it and got the much more expensive DA*50-135 instead. I also added the K200/2.5 and F*300/4.5, which really
do produce compelling images. But all of those are down the road if you ever decide it matters that much. For now I'd get the DA55-300 or F70-210/4-5.6 and focus your money on the 17-70 or 17-50 range.
The F24-50/4 or A24-50/4 and FA28-105/3.2-4.5 (I really think it's the best 28-105, although apparently a few people got bad copies) are also great yet affordable lenses that can create compelling images. And while we're on the subject the Cosina 100/3.5 macro (available under many different brands with either AF or MF) is a great value, as is the A50/1.7 (each a little under or over $100, depending on whether it has AF in the case of the Cosina). Do your research and decide which ones you like by looking at the images:
PENTAX : Select a PENTAX interchangeable lens camera or a lens model Pentax smc P-FA 28-105mm F3.2-4.5 AL IF Lens Sample Photos and Specifications Advanced Search