I did the cheap Chinese eBay radiators on my old 2011 YX450, and they worked fine. What I didn't like about them is that they all seem to be oversized. The radiator guards or cages don't seem to fit any of them very well, and often the quality of the Chinese cheapies can be anything from pretty close (some minor grinding required) to they don't fit very well at all no matter what you do.
There are some other options, but I think when I finally do need them I'll do OEM from somewhere like Parzilla. Yes, they are much more expensive that way (although probably only half of what they cost from a dealer), but you can put good guards or cages on them to protect them.
I'm sure you'll get lots of replies and personal experience, but here are a few options:
eBay specials
GPI
Warp9 radiators (oops, read on another post that they no longer make these for the KX500)
You can also look into getting your older radiators repaired by someone like Mylers. (
http://www.motorcycleradiators.com/)
