As Kjell stated, that's a very good lens. It's actually the same optics and build as the A*300/4, but without the auto exposure contacts. It was, indeed the first "star" lens, and was a distinct departure from the much larger and heavier "K" 300/4.
Pricing, IMO should be under @ $420 USD in EX condition, the more under, the better. Realize that I'm pretty cheap though, and market prices have probably gone up a bit from when I was in the market.
The lens is very sharp wide open, but suffers a bit compared to later AF models (F*,FA*, and DA*) because of lesser ability to control CA/PF in high contrast situations wide open, and because of its long minimum focusing distance (@ 13 ft compared to 6 ft for the F/FA* and 4 ft for the DA*). The CA/PF isn't horrible, it's just not as good as the AF lenses with their expensive ED glass. This, and the A*, of course, are the best mid fast MF 300mm lenses in the K mount (and one of the smallest, lightest pro-quality 300mms ever made).
"mole" also has an A* 300/4, and his looks like someone tried to clean the front element with a cinder block (Roy had a similarly damaged one), and both of them took some amazing shots with them stopped down some. It can also make an excellent AF 510mm/f6.7 with an F 1.7x Auto Focusing Adapter.
If you want a comparatively inexpensive premium quality 300 prime that's small enough to pack reasonably well, this or the A* are the ones to get.