Why pay...it will make them rich?
I am not sure anyone should ever use an agency...I lost about 55 million using one.
However, the thought about having an idea and that is all you bring to the table is a hard sell. It is like hitting the lottery if you can come up with an idea and that is all you do...and somehow it makes you money for coming up with it. How many times have you heard someone say...hey, I thought of that. The one who pursues their dream, concept, insight with vigor and passion, determination with doing the right steps, gaining insight and sometimes taking risks can achieve success, sometimes. There is a lot of work to bring something from concept to the market, the more you can do yourself to bring it from the start to the finish the greater your reward in the end. This can be a life changing event during the whole process, usually for the better even if you fail. The knowledge you gain from each step can help you help others get farther or take your next idea across the finish line!
Good luck, just don't give up!