Patients aren't usually willing to pay cash for service for medical care. There are a few exceptions...cosmetics, pain management, and sex life.
With the direction of medicine (decreasing reimbursements, decreased time with patients, increasing overhead, increasing regulation)...a smart strategy is to find a profession that you can make a living even when the whole system goes to complete ****.
Cosmetics: Dermatology, Plastics, Urology, ENT (if doing OMFS stuff)
Pain Management: Pain, sports medicine, PM&R (maybe anesthesia...though less traditional), OMT
Sex life: Plastics, Urology
As you can see...Urology gives you two avenues to cash pay...not bad.
Most Urologists I know work like dogs...but the truth is that the profession gives you flexibility to NOT work like a dog if you don't want to. That is not the case of most surgical fields.