Questions regarding popular franchises

I just got a ps3 not too long ago and tried out a bunch of ps3 demos, where none really hit me good enough to go out and buy the game. So I was thinkin of buying some ps2 games who has sequels announced, I wonder though how potentially important these games are for the sequel. The games are:

Devil May Cry 2 & 3

GTA Vice City/Liberty City stories

God of War 1 & 2

Also I was wondering if anyone knew where to get these cheap (under 15 $US would be a nice spot). I live in California btw. Oh and add MGS3 and Okami to my shopping list. I tried gamestop/ebgames but used games aint really cool if it's only 2 dollar difference (talkin about god of war mostly). Anyone please help me with one of these.

you dont have to play Devil may cry 2 but you might have to play Devil may cry 1 and 3 because Devil may cry 4 is before part 2.Luxen90

So the story in Devil May Cry 2 is not important at all?

dmc 1&3 part 2 suks

gow 1&2 kicka$$

and I dont know about gta