CR-4 like
this one? I have this scope and it is a great starter scope for a refractor with good compromise between price and quality. The mount is actually not a bad mount if tweeked a bit and telescope's chromatic aberation (blue fringing colour notorious with achromatic refractors) in not too bad compared to other 4" scopes.
C6-R
like this? I've used one identical under a different name and found the scope just a bit overweight for the mount (but then I was looking at it from a photography perspective). Visually it was fine. I found more chromatic aberation compared to the above 4". It is also considerably heavier. I much more prefered the 4" even though the 6" has a larger objective.
The
LX55 AR5 is now superceded by the
LXD75 AR5
I've never used one but I would imagine it would be very similar to the 4 and 6 inch refractors.
Not sure what prices you should be asking, but I believe they are overpriced new as it is. Recently a 6" Skywatcher went for
$650