Disclaimer up front: I don't have the book.
"The Art of Michael Whelan" is from 1993, so it won't contain any work he's done after that.
Since you mention it costing $400, I assume you're speaking of the
Signed & Limited Edition he sells through his website. That's something altogether different from the regular edition (that seems out of print, but is
readily available through the Amazon marketplace and the like), and for what it is—a high-quality, limited, unique edition—$400 seems a reasonable price. If it's worth $400 is a different question altogether.