Building a bike will cost you more compare to buying a bike all ready put together . With that said , building your own bike give you the chance to chose the components that you want and help with the idea of being custom made . You should support your local shop ,but there nothing wrong with shopping online for prices and compare . Your price range will be between 300 - 400 dollars for either bike.
You can use the U-lock with the cable , use the u-lock in the place of key or combination lock .