I received a gift card for Christmas to home depot here in Canada. My local store has a 1″X10″X4′ pine shelving for about $3.22 a board. I needed a 27″ piece at the full width. I managed to find a few boards were I could get my 27″ pieces knot free, which in my local store is hard to do even if looking at the full length highly priced boards. These shorter boards fit in my car (which can hold 8′ boards). Plus, the off cuts I can rip to widths as to avoid the knots for other projects.
If you make the bookshelf less that 4′ wide it might work.
I am making the small dutch tool chest from Chris Schwarz article in Popular Woodworking Magazine. It will hold all my tools and is a fairly simple construction, which is important as I am moving in 2 weeks and I only have 3 nights a week to work on it. I think the design works better for my needs than Paul’s design, but I use all of Paul’s methods.