If you buy one from somewhere like Gamestation you can get extended warranty plans that cover in the event of a failure. It also covers things like broken controllers and so on. Not sure if its available on second hand ones or not.
Be wary of controllers passed off as Sony ones on eBay. They look exactly the same but a different letter in the serial number gives them away as fakes. They will not work with the V3 software update.
I got mine a couple of years ago and paid £170 for it. Its worked flawlessly since I got it. Has a 80GB HDD in it. Not sure what the new slimmer ones fetch. Also I dont know if the newer ones are backwards compatible, but out of the older ones only the 60GB version was able to play ps1 and ps2 games IIRC