More pixels means you can print and show bigger pictures without loss of resolution, but if you never print/display anything above say about 1920x1080 then even 10 megapixels is actually quite sufficient. Its not the technology that makes good pictures but the skill of the photographer in taking the shot and in post-production developing. People get hung up on having big numbers.
When you take a big pixel size image and you show it online by shrinking it with compression you lose information anyway.
I bought my K-5 for about £320 after the import duties were added, that was just the body. It had only been used for about a couple of thousand shutter actuations and they are generally good for 100k. Got a 100-300 mM zoom lens of ebay for £85 and a 18-55mM lens for about £30 too.
A review http://www.dpreview.com/reviews/pentaxk5