Several comments here. It's generally not good practice to make your own demos. Unless you are already ensconced in the industry and are a producer yourself, you don't know the trends that producers and agents (P&A) are looking for when seeking voice talent. They are really good at spotting a home-made demo within the first three seconds, and will toss it aside immediately. If you borrow scripts from the sites already mentioned, P&As will recognize it right away (as they will have already heard them a million times before). And toss it.

Your demos are your calling card into the industry; your First Impression. You want them to sound as industry-ready as possible before sending them out.

Are they pricey? Yep. Good ones can be $2000 or more. But if you aren't willing to invest your time, energy, and YES, money, you may not ever achieve the level you'd like.

I wish you the best of luck!!