Hi,welcome here

I guess that chinon lenses are M42,so all you have to need is buy an adapter to them.there is a pentax one,wich is said to be the best,you can find it for cheap in the market place,ebay,etc...
I guess that is a very cool price on the K100D,I bought my self a k110D used with the sigma lenses on my sig for 250eur.As you may know,the k110D=K100 - Shake Reduction.
I prefered Pentax instead of Canikon because of the following reasons:
*Compatibility with M42 lenses (although on canon you have lots of adapters,you have to choose the right one on millions of china made adapters,on pentax,you only have to chose the original one

)
*The price used - as in Portugal there isn't a lot of people choosing pentax they go into slighty lower prices than canikon.
*The fact of using AA batteries instead of a battery.
*The huge amount of old cheap and awesome pentax mount lenses available on the used market.
*The reliability of the brand - after lots of reading in portuguese forums I never found a pentax dslr with problems.
Well guess that's all,hope it helps