Here are a couple of sites I came across that compare the price of wow gold across the various virtual currency providers.

URL: http://www.world-of-warcraft-gold.com

World of Warcraft is the first massive multiplayer online role
playing game that combines considerable depth with intuitive gameplay.
Thus, hardcore gamers and casual gamers are both able to enjoy this
game. World of Warcraft is just over 2 years old and has over 8 million
subscribers world wide.

The web site World of Warcraft Gold
Price List Guide was setup to cater to this large group of players.
This site focuses on the practice of virtual item selling; it provides
an ever updating list of World of Warcraft gold prices across a cross
section of gold sellers. There is a section on World of Warcraft Power Leveling about the do's and don'ts of using this type of service plus a recommendation on which company leads the way in this service.

One of my favorite sections on this site is the collection of World of Warcraft Videos
and fan made movies. If you need a laugh definitely check this section
out. Overall a good site for both new and experienced players. Spending
a bit of time on this site will definitely help you learn to improve
your game play.

URL: http://www.wow-gold-price-list.com

It’s safe to say the video game community is infatuated with WOW.
GamerMag says "WOW is the massively multiplayer online role-playing
game that nearly everybody can enjoy, and is a shining example of the
game developer’s art." And GamerMag said: "No game has done more to
make MMORPG a household word in North America than WOW."

There's a whole language and culture involved in WOW, which might
make the beginner a bit squeamish when he or she decides to take their
first trip to the war-torn world of Azeroth. With that in mind, avid
WOW fan Mark MacKay created the website WOW Gold Price List, an oasis for players that’s complete with all the required WOW information and analysis.

This site breaks down the facts with WOW information and articles on
gold purchasing. The home page also includes links to movies, WOW Power Leveling providers and, most importantly for the beginner, the WOW Explained
link. This page breaks down the character names, the playable races and
gives an easy-to-understand tutorial that outlines all the game’s
basics.