It kind of depends on your intentions, and what you want to spend...

Not sure what powder coating would cost,
but I'd bet you could buy a nice set of wheels cheaper.
I don't see an issue with spray paint.
I sand blasted and painted a set of rims more than 10 years ago.
Used cheap store brand spray paint.
Those rims show less signs of rust than any 10 year old factory wheel.
They have been used for several years in the snow and salt of Wisc. winters.
Like always the real trick is getting the metal clean first.