I scored big-time at Staples yesterday: They have a Sharp calculator, the Elsimate EL-344R, for $11. This calculator is perfect for the shop as it has 44 native metric/imperial conversions built in, the ability to program a new conversion rate, and will also work with imperial fractions! (ex: 3 1/4 + 5 9/16). It also has a 10 digit display instead of the standard 8 digit, and is dual power (solar and battery).
As I'm working on metric engines as well as American engines, the metric conversion ability is going to be very handy!
I highly recommend it for a shop calculator, as you can't beat the bang-for-the-buck.