www.dealextreme.com is one of the cheapest. I got my cousin an Acekard 2.1 from there. But the shipment, if you choose the free option, will take up to 2 weeks to arrive. It took 1 and a half weeks to get to me in England.
I got mine from RealHotStuff.com because they're located in the US (New Jersey), they had FREE USPS 1st Class Shipping (I ordered Monday and got it on Wed. I live in CA) all for exactly $19. RHS also guarantees that the Acekard is the Acekard 2.1. The packaging was pretty good. It was a medium sized cardboard box containing the super-small Acekard box. The SD Reader is not the Acekard SD Reader but it is extremely sturdy and works well.
If you don't mind waiting, then I suggest DX. But if you can spend an extra 7 bucks to get it to you a week early, then go for RHS.
I ordered from DX, it took quite a while for it to ship (almost two weeks). It shipped last Tuesday, and I'm expecting it either late this week or early next week. If you want to pay little, but wait a while, go the DX way, it's definitely legit and you will get an AK2.1 eventually. If you want to pay a bit more, and want it to be quicker, realhotstuff.com might be your way to go.
I've had good results with some of the recommended sellers on the main page here, like Dealwoot. I tried ordering from Dealextreme one time and although I can't dispute some of their prices, their support is something else entirely. After a couple days of mounting anger over scarce communication on their part, I finally forced them to cancel both my concurrent orders which was an ordeal in itself due to a conflict that arose with Paypal. I've never had this kind of bother with online transactions before and since Dealextreme.
So on a personal note, it would take very special circumstances before I consider doing business with them again.