If you go to the computer centres, there is likely a shop or two selling 2nd hand models. There should be 1 shop in at least Wanchai and Mongkok that I have seen before.
I had a quick look round the Wan Chai centre a couple of weeks ago, there are a few places sell second hand machines that vary from exdemo to pre owned. I don't recall seeing anything prices as low as $3000 but it looked like there were perfectly serviceable machines around the $4500 mark.
Wanchai computer centre has a few shops dedicated to selling second-hand parts and accessories like chargers and batteries.
There are also some shops selling legitimate software and one or two selling illegal copied software.
298 Hennesey Road is an older-style computer centre and has more illegal software and parts for d.i.y.