Definitely would pay for feedback.
I've applied for pretty much every job available (driver, guard, conductor, signaller etc) across different TOCs over the last 6 years or so but have never made it past the paper sift.
I even paid for my cv and cover letters to be tailored to me by a hr company in the hope that it would give me an edge but obviously didn't help.
I'm a transport manager, IOSH managing safely and neebosh safety trained so should look good on paper yet just have no luck getting past the sift.
Surely one day I'll get a chance.
That suggests your initial applications are lacking in some way.
You should pay very close attention to your application forms. Are you proof reading them (consider getting someone else to read them through “cold”)? Are you answering the questions actually asked? Are you selling yourself properly? etc.