First Arduino Project.

First time using a Arduino and it's for a school project. I have a uno starter kit (but willing to upgrade) and for my project I want to make something VERY similar to the arduino laser harp video that is floating around. However, I really have no idea where to begin. Such as a decent website that I can purchase items from that is trustworthy and in the US.

I have little knowledge of C+ but am willing to make this happen. I guess what I'm looking for is how complex this is going to be and what price range im looking at?

Video below, Sorry if not embed properly.

Edit: Thanks for any help in advance.

Quite an ambitious project for someone who is just starting and "has little knowledge of C++".
I'm not sure how laser harp actually detects which beam is broken, but if I remember correctly it is done with a video camera.
Arduino will not be capable of processing video, but it may be possible to use some LDR to detect if it is broken (given powerfull enough laser and non-intruding ambient light.
I would start by figuring out how to draw "strings". That alone should be a challenge for a beginner.