A good powder coater will do all the prep for you. Media blast to remove old paint and rust, and then masking and plugging. Talk to each potential PC to see if he really know bikes and frame materials. I have heard stories about over aggressive blasting.
A local shop here does excellent work and charges $65.00 for frame and fork. That is for a standard color that he stocks and then a high gloss UV protective clear on top of the color. If I want a custom color I just buy it myself at an online retailer and provide it becasue sometimes he is forced to buy unnecessarily large quantities from distributors.
This is a really good place to buy powder in small quantities.
https://www.powderbuythepound.com/
Painting becomes expensive when you get up to really good workmanship and paints. It's obviously more versatile because you can do endless amounts of multi-color designs and art work.
I prefer powder because I am a monochromatic, logo hater.
And a good powder job looks wet, smoothes out less than perfect welds, and is tough as nails.