Thanks everyone for the replies, I've had a look round on various websites and I've found a 135mm f/3.5 for around my price range which sounds good and it's in very good condition, I've also found a couple of 50mm f/1.7s which I will keep an eye on to watch the price. As for a wide angle lens then I will look for those mentioned (28 and 35) as f/3.5, they often seem to be regarded better quality than the f/2.8s. I am familiar with the pentax forums reviews and they are very useful.
I'll also have a look at some of the M42 mount lenses as they also seem to be quite popular. With the zooms I've been told that they aren't great but I'm nothing of a professional photographer so I'm sure any of the zooms mentioned like the 75-150mm would be great for me, as long as they're a good price.
Finally with the camera I'll have a look for someone in my area who could service it, but if it is too expensive to repair then I think I could get a new one for a similar price or cheaper on eBay.