UpWork is a well-known website used to find and hire freelancers and can be a great way to get a book written inexpensively. Fiverr is also a great website where you can get a book cover made for only $5-10. However, it's important to understand that you get what you pay for. Your goal should always be to publish a quality book that your customers will benefit from.
There are exclusive writing services that some of our students use that are only available to members of my Mastering Book Publishing course. I'm unfortunately unable to share the specific companies and services that I use outside of Mastering Book Publishing, out of respect to the members of my program and because I don't want to cause any further delays as these services can only handle so many orders.