IMHO, you are better off buying new ones.
For the price you will pay for used ones from somebody, what is a good deal like $20 each, plus about $10 to ship. For the extra $15 to $20 you have to pay to get a new one, you get new bulbs with full life.
Any used one you get will most likely need new bulbs now or soon, then you have to pay almost as much as the fixture itself cost to replace them.
In reality, I feel you are way better off buying new, they are not that much money.
I could have answered to you in this message that I have two of them and sold them to you for about $20 each plus shipping, and what I would have done was sold you mine and bought two more, and I think it would have been cheaper for me to do so then for me to replace the bulbs that I feel I will need to do in less then a year.
I could get two new ones for about $100 after ship (unless they went up to rediculous prices lately, I have not checked) and after you paid me the $40, I would have laid out about $60.
It will cost me $10 per bulb from Big Al's plus shipping so about $50, so for $10 more, I could have gotten two new, you would have to pay that same $50 to replace the bulbs by the end of the year and would not have saved anything since you paid the $10 for shipping from me.
Unless you can only afford the used now and later can replace the bulbs and it is the only way for you to get the lights now, then go for it. If that is the case, I can sell you one or two, but you know what I am going to do.