All FBI Background Checks must be apostilled in order to get your E-2 visa. However, if you're in a rush, check these guys out:
This is not a paid advert. I needed a last-minute apostille. For two FBI background checks with an apostille, the fee was $166 (and the additional cost of Fed-exing it to Korea was $70.00) and I had it within five business days.
On the left-hand side of the site, find links to all the document processing paperwork you need. Use the phone number on the docs to call them- they are super-friendly and very responsive.
It relieved a ton of my stress to use Washington Express Visas. I think if I had to go through the process of getting a background check apostilled again, I'd use them instead of handling it myself.