The K1000 was made and sold for many, many years after the KX was dropped from the product line. A K1000 of roughly the same age as a given KX is going to have the exact same shutter mechanism. If two cameras sound different, it is likely that either: a) the K-1000 is newer (and potentially made of vastly different materials) or b) one of them has worn mirror bumper foam. Some of the shutter noise is actually mirror slap. This is especially true when the mirror foam has deteriorated.
The KX was the first "real" camera I bought. Way back in 1975, I went to the store with the intent to buy a k-1000 but, that wily sales man "up sold" me and I went home with a KX. I still have it today. I've also owned at least five K-1000 over the years. Yeah, they are similar but, the KX has several features which set it apart.
The KX has match needle metering where as the K-1000 has only a very simplistic "center the needle" meter. The light meter in the KX is technologically superior to that of the K-1000 and the meter on the KX can be turned on and off with a switch (actually by pressing very lightly on the shutter release button) but the K-1000 meter is "always on". The KX has a self timer, depth of field preview and mirror lock up. The K-1000 had none of these features. he KX also has full exposure info in the viewfinder - you can see the shutter speed setting, the aperture setting and the light meter reading all in the view finder. Not so on the K1000.
60 euro for a KX seems about fair - assuming that it comes with a lens and that it is in excellent mechanical condition and reasonably good cosmetic condition. If it needs an overhaul, then 60 euro is too much.