.... how hard can it be
Harder than you think...
I have only ever, once, sprayed a frame, and it looked ok from a distance, but wouldn't pass close inspection (it is currently in the care of CL OTP).
For my money, by the time you have paid for primer, top coat and laquer, then totted up the time it takes you to sand, fill (if necessary), sand, prime, sand, prime again, sand, paint, sand, paint, sand, paint, lacquer, sand, lacquer, sand then leave the frame for at least 6 months for the paint to properly harden, it is cheaper and easier to just send it for painting or powder coating.
The last frame I had painted (for Mrs T) cost me ~£100 (IIRC) for the paint (there was a lot more work the frame needed so the final bill was way north of £400) but there is no way on this earth I could have even gotten anywhere close to lovely finish on that frame (it was done by someone who does this kind of thing for a living, has done for a long time and is a member on this here forum)