When I first started LAing for others, I charged a very minimal fee for quilting. My friend entrusted her quilts to me to learn on and only paid about $20 to $30 per quilt basically enough to pay for my thread and a token amount for wear and tear on my machine, my time and effort. I made sure she understood I was new and just learning and she took a chance on me. I will be forever grateful for that opportunity because I would not be the LA quilter I am today if not for my friend Meg entrusting her first quilts to me. It was a good experience too, because Meg was also a beginner quilter so I was exposed early on to wonky, out of square quilts and learned a lot from doing her quilts.
Only you know if you feel you are good enough to charge what other professional LA quilters in your area do. Remember that word of mouth can be your friend or your enemy. So if you do a job that the maker is not happy it can snuff out your budding career in no time flat, likewise if you are good you can end up with many new clients just as quickly.
To your original question... As others have stated it varies by region. In my area, a simple all over meander or open continuous quilting is .01 per square inch. A simple Panto done E2E starts at .015 and more complex panto .02.