Hey Rachel,
Depending on how resourceful you are and how much time you have, paying for a well designed cover letter/resume may not be worth it. The beauty of professional services is that they do it quickly (compared to you doing it perfectly yourself). They also create a very nice design and know exactly what words to put down.
Now the problem is that if you decide to change career paths later on, you will have to pay another big amount to have your resume done for you. Everything that they have done for you, they do not explain – they just create a perfect version from what you had before and leave you there.
So only take this service if you are 100% confident that you will stick to this career path.
Nevertheless, there are other options available if you seek career help.
Me personally, I have worked with a company called Definitely Hired (definitelyhired.com) over the phone, and they perfected my resume/cover letter/interview over the phone while telling me exactly what I should have written down or not. This is beneficial for me because not only did I get the bank job that I wanted, but I also kept the information, and was able to help my friends in need without them having to pay.
I would strongly suggest looking into other ways, such as the company I dealt with (Definitely Hired), because out of thousands of resumes (that get THROUGH to the hiring manager after online screening), managers take a quick glance and move on – for which reason it is crucial to make your resume stand out.
Best of luck!