I wouldn't pay someone to look at my PS. Do you know someone in academic medicine well? Either from rotating at a hospital during 3rd or 4th year, or personally? Or even a Dean or some in a similar position at your medical school? They would help you out for free if you scheduled a meeting with them. I ended up asking my clerkship director from one of my 3rd year rotations who coincidentally was also a residency program director for his department. I think it was way more beneficial talking to someone who actually knew me well. Plus...it was free 🙂