Cost is all relative, if you aren't taking in to consideration the extra equipment you are using. Some will say that you can get great taste with extract if you do it right, which includes a lot of special handling of LME, freshness factors, etc... All grain is more of a challenge, but it is easy to get great results... it's easier to manipulate a recipe using what you have on hand... so yea, there's a lot of reasons to go all grain. Also a lot of reasons to stay extract.