If most of your pieces are under 8.5" x 11" , a flatbed scanner is definitely the way to go. That's what I use for the majority of my pieces, and it works the best. You don't need a super high-end scanner, I use an all-in-one printer that has the scanner built in, and it cost me about $60. Just be sure to scan at a high enough resolution.
Scanners larger than that tend to run very expensive (I believe 400+$, depending on the size), so if it's larger work, you may want to look into getting it photographed, or taking it in to a print shop to be scanned for a fee