You can buy a TI-81 graphing calculator by Texas Instruments on Amazon.com or on eBay. Because the TI-81 is an older model that is no longer manufactured by Texas Instruments, it is not available new or through traditional brick-and-mortar retail outlets.
The Texas Instruments TI-81 was first introduced in 1990 and has since been superseded by the newer calculators TI-82, TI-83 and TI-84, therefore it is no longer manufactured and not available new.
The TI-81 is available used, albeit indirectly, through Amazon.com and eBay. Using Amazon.com, a purchaser can order through a number of different third-party merchants that sell the TI-81 in used or refurbished condition. Some of these merchants have Amazon.com storefronts but do not have their own websites and therefore don’t offer goods for sale except via Amazon.
Because eBay is an online auction site where private individuals can sell their goods, prices and availability of the TI-81 graphing calculator varies depending on who happens to be selling one at any given time. In addition to Amazon.com and eBay, the TI-81 Graphing Calculator by Texas Instruments can also be purchased at Bonanza.com, an online marketplace similar to Amazon.com.
Because this calculator is available exclusively used, availability at all retailers varies. In order to ensure that you’re getting the best price and condition, be sure to compare various retailers and to look at the Amazon.com reviews of those retailers.