Here is a YouTube download trialware for your attention. Like the Title says you can download your favorite YouTube videos for local consumption again and again instead of having to incur bandwidth charges for it each time. This is a paid app so you are allowed to download and give it a try. Eventually you’ll have to pay for it if you decide you like it.

Here is vendor description from the Windows Store:

Tube Download allows you to download YouTube videos on your device, so you can watch them again each time you want and each time you are offline!
Videos will be downloaded in Video Library so you can play them simply clicking the Video tile on your Windows 8 start screen.
Tube Download can download HD (1080p or 720p),  HQ, or LQ videos depending on YouTube availability, but obviously you can also search and watch a streaming video without downloading it!

Live Tiles and Toast Notifications when you completed a download!
Background Downloads!
Bigger video tile when a video has many more views than others
Tap the toast to immediately play a video
You can share videos

You can download the app via the source below.

Source: Windows Store