OT Need advice: Compact Flash Cards for Audio storage

["Rick Walker" <looppool@cruzio.com>]

I purchased an M Audio Micro Track 2  Portable Audio recorder today
to begin recording all of my concerts on my upcoming European tour
and the guy who sold it to me said that he used a 4 gig Compact Flash card
with it which, he said,  gave him the ability to record two live concerts 
sets
on it without dumping memory onto a computer.

I went online to find 4 gig flash cards and found
ones that cost $21.99 (A DATA -
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3281680&Sku=A208-1172)
and ones that cost $89.99 (San Disc Extreme III  -
http://www.memorysuppliers.com/compactflash.html?gclid=CKK79Mnwi5ECFScXagodeC3PFg

Is there a huge difference between these?

Are there things to be worried about in buying CF cards?

Things to avoid?

Do you all think it would be better to buy a couple of 2 gig cards instead 
of
one 4 gig card?

I'm a newbie when it comes to this subject and could really use your 
collective
expertise on it.

Thanks, in advance,

Rick