If you are comfortable with a hand grinder, Porlex grinders [1] [2] are excellent. I use one to make a coarse grind for the french press. It's gotten used 4-7 times per week for the last 5+ years and still going strong.
On topic of best purchases under $100, suppose you regularly boil water for coffee or pasta but don't own an electric kettle, consider investing in a cheap white plastic kettle for $5. Fast and energy efficient way to turn electrical energy into boiling water.
I think _good_ depends on your expectations. We have the eureka mignon hacked with a bigger dial and custom burs. Still not amazing consistency. Looking to upgrade in the next few years.
