Im going from one extreme to the other here .. my usual macro to long range. Anyway ...
I bought a fully manual Pentax 300mm telephoto prime lens off Ebay a few weeks ago for £130, it was supposed to be in mint condition having only been used a "handful" of times so for the price was a good buy, even for a 30 year old lens. Upon arrival I can honestly say it has seen better days, although not battered by any means it was certainly not as described (scuffs etc and a small mark on the glass) so after a bit of haggling I got £80 refunded from the seller. (Lucky for me he had high feedback and 100% so obviously didn't want to jepodise that).
Anyway, have been having a play with it over the last couple of days and here are a couple of shots with it, I have to say I am pleasantly surprised by its performance. It seems quite sharp close up and wide open (second shot) gives a almost surreal look to the flower on the tree.
The only thing against it though is that it is made completely of metal and along with the K10D (which is one of the heavier dslrs out there) it weighs an absolute ton.