I think there are several things to consider. Will these be straight slimlines or contoured? What kind of material will you be using for the blanks? Wood: Exotics or domestic? What kind of finish? CA, Mylands, Deft, Enduro, Hut? Will these be engraved? Do you need a box or pouch for each pen? Some of these things can add up in cost and time.
$20 a slimline for 3,000 is a good deal, but you also need to understand what would be expected of you for the end product. If it were me, I would do it, but I know I would have to get help. I am sure you could get additional help outside of OH if you need to. Johnathan gave some good advice. Make sure this is for real and require a good chunk up front. Enough to take care of materials and some of your time. Also write up a contract spelling out delivery times and payment timetables.
Just a few thoughts that came to mind. Good luck and let us know what you decide.