My take is different from the majority here.
Why would I want another person to write about my project? I know it takes time to write, but describing thousands of ways your project IS a big part of the project.
Personally, it's hard to justify to pay for a person to evangelize (i.e. write) about my product, specially starting-up.
But hey! That's me.
After all, the one of the best salesman and evangelist of all time
, did wrote his stuff, even though due to the size of the company he ran, most surely professionals writers helped him, nevertheless it was his vision put on writing.
My 2 cents.