In the past few months, we have covered a bunch of awesome electric skateboards. You could always build your own though. comsa42 has published a guide that shows you how to build your own electric skateboard with regenerative braking, an on/off switch, and a Bluetooth smartphone controller. It has a max speed of 30 km/h and a range of 10 km at full speed.
The above video shows this electric skateboard in action. You are going to need 5000mAh batteries, a Bluetooth controller, a brushless motor, and a few other parts to complete this project. According to the developer, you should be able to pull it off for about $350. More information is available here.