i just saw a thread about this yesterday and it had some pretty cheap 4gb sticks but i can't find it now, i'll see if i can find the sticks for you thought just give me a sec.
I think cheap Msd cards come around if you wait. As some said, you can go to amazon, but I know I like going to Microcenter (if you have one around you) because they usually have the cheapest prices unless someone is running a sale.
30 bucks. If your willing to wait you might be able to get it for cheaper, I think i got mine for 25, but I dont remember. The nice thing is that you can buy one adapter, and get a cheap card for now (15 for the 8 gig) and buy a 16 later. Either way, the adapter is nice because it gives you options.
It treats both SD cards as a unified memory bank, so you're essentially getting a 16GB memory stick if you get two 8GB SD cards. Way cheaper this way! Or at least, it used to be, prices on 16GB cards have really dropped. Maybe I should upgrade to 32GB...