Thats a hard question for me. Becuase I make cards AND scrapbook, I usually buy sets. It seems like I can buy in bulk and save money- so with my leftovers, I can do a lot of projects. I like to post lots of projects on my blogs too so having that sources is always nice.
If you just scrapbook though, It probably would be ok to just buy a few sheets- Especially since it is halloween and it only comes once and isnt HUGE then you may not need all of that paper!