As the saying goes -- "How much have you got?"
You can spend thousands on amps if you want to, but if you're just looking to get some good thumpin' out of your sub box, you can get a 550W Crunch amp for $98 from walmart (
here) and you can get a 10-Gauge hookup kit for another $14 (
here)
Your speaker box is rated at 400W drive, 800W peak. You dont want to drive it with an amp smaller than 400W, or you can damage your speakers by overdriving the amp.
You can sure spend more than $112, but that's a good basic setup for someone on a budget.