In this gallery, few pictures shooted with my ( old ) zoom Pentax FA 100-300mm f/4.7 – 5.8. There are two models of FA 100-300mm, here it is the silver version ( may be the best of both ).
I bought it for 100$ ( not expensive )... quite new and I was very surprised by its really good performs at all focals. I think that this lens ( now discontinued ) is a very good choice for a very low price. Sure its plastic construction seems a little vulnerable but in fact it gives a solid feel. It is also very light and little so it has always its place in my bag and helps me in many situations.