With a monochromatic color palette, the brown boots inject color, variation, and intention into the look. Black boots could never provide the richness the brown does.
I've been a fan of JCPenney's Stafford brand since high school. Their Deacon boot is a perennial favorite, loved by internet style aficionados of all income levels. I recently purchased mine on sale for only $60, a great deal considering they're a steal at the regular price of $100. They also have a cap toe version, the Gunner, that you can check out for a boot of a similar profile. If you like the wingtip, Sebago also makes a version for $157.