Tim cost certainly has to be taken into account.
2004-2008 is getting on the old side. In my building it would be time to sell. A rebuilt spindle is $10K. If its PC it will have an XP computer, that can be an expensive replacement meaning not $500 but a few thousand once you get help loading the software. If the linear bearings, ball screws and/or drive racks are worn the whole thing becomes sloppy and not in a predictable way.
I would not buy one unless you see it run. If you can bring a CNC technician with you to see it that would be better. Creating a test part drawing you can measure would be helpful. If you have an 8" or 12" digital caliper make a drawing of a 8"-12" square with 8mm holes drilled 1"+4mm from the edge all around. Ask the owner to cut you a sample part from MDF and measure it. It won't be perfect but how imperfect is it?
Then there is the question of software. Used may come with software. Most machines have some kind of software you can make one off parts. That is something to consider.
I have not shopped for new machines in this price range but there are smaller machines that might be a better choice. You can get your feet wet see what these machines are capable of adjust from there.
We kept the machines we used to use pre CNC for a while. After they collect dust for a year you end up selling them and become dependent on the CNC. Then the reliability of the CNC becomes paramount. An older machine tends to be less reliable.
Finally what type and quality of service is available near you? Depending on how handy and computer literate you are you might need some help refurbishing or keeping the machine running,
Off the top of my head if I was considering what you are doing these are the things I would be considering. As many have said I wish I had bought A CNC machine sooner. The amount of work it can do is amazing. Mine paid for itself in less than a year.
Good luck with your decision.