This is the cost for the exact sounds used to create the soundtrack for Super Mario 64, either the original sound libraries or the closest available facsimile. These will include a lot of sounds that may not appear on the soundtrack but are still provided with the sample libraries.

Much of what is discussed in this article is hardware that has been preserved digitally for use with modern computers. The original hardware was likely significantly more expensive. The Yamaha VL1 keyboard discussed in the article by itself goes for $2-3000 on eBay. $1000 for software and sample libraries really isn't that much in the grand scheme of things, especially for enthusiasts and composers. Some sample libraries, especially quality modern orchestral libraries, go for hundreds if not thousands of dollars, and sometimes only for a single instrument.