Walmart offers the Texas Instruments TI-89 Titanium Graphing Calculator for$104.79 with free shipping. (Amazon charges the same.) That's the lowest price we could find by $26. It's ideal for calculus and features a USB connection and I/O port for communication with other TI products.

Update: It's now sold out at Walmart; however, Amazon still offers it for $104.79 with free shipping.