I just had my panels painted, so did a lot of research on this.
I found some great posts after google searches where people used rattle cans to get near-professional results, but it was a huge time investment (and for me money investment since I did not have the supplies or tools). There was multiple stages of cleaning, sanding, wet sanding, buffing with buffer tool, etc. I once painted a guitar without the sanding and buffing steps and although I was very careful and used expensive paint and clear coat, it very much looked like a rattle can job -bumpy texture and unprofessional. Given the time and money investment, I went with a professional body shop this time.
I found I could get better quotes after I took the panels off, cleaned them up a bit and brought them to the shops in a bin. This way they can see how little there actually was to paint.
Quotes I got for pieces for an Agility (front fender, two fairings, and front panel surrounding headlight) were:
$500 - respected body shop
$350 - bodyshop
$275 -Maaco
$350 - another respected body shop
I went with the last quote and one week later, they were done and looked great. Totally worth it for me.