I was thinking of starting a website that provides price listings of certain online in-game products (items which can be used within a game that must be purchased using real money). I was planning to get the price listings from two different sites that display this information and was going to mention that the information was obtained from those sites. Is this legal?
Not everything is capable of being copyrighted. According to Circular 34 lists are generally not subject to copyright. In addition keep in mind that to be copyright the subject matter has to be one that is result of creative effort, ie "...original literary, musical, pictorial, or graphic expression." I would think that a price list does not fall under that category because a listing of numbers and items is not such an expression.
However, keep in mind how easy it is for anybody to file a DCMA take-down notice. It looks like Best Buy did so in 2006, to prevent their "Black Friday" sales prices from being publicly revealed, as per the Ars Technica article, Best Buy tries to copyright sales prices.
In short be prepared for a DCMA take down notice directed at your website. Be aware that although sales price lists may not be proper subject of copyright, this does not stop this author of the price list from bringing suit, and perhaps under other theories of recovery other than copyright infringement. See the Skiplagged Complaint for an example of this type of litigation.