If you were just going to paint it black anyway I would have just sprayed it with rubberized undercoating. More durable against scuffs and scrapes too being a lip. It will also hide imperfections because of the slight texture and semi gloss finish. Also easy to touch up, and contain over spray vs something more airborne like spray paint.
If you are set on painting it yourself it depends on how good of a finish you want vs effort.
At a minimum hit it with a fine scuff pad and then wax and grease remover.
Next level would be wet sanding, depending on how rough the surface is you would start with either a 400 or 600. Make sure you use a nice sanding block for the flat areas. After the 600 then scuff pad and wax and grease remover.
Last level would be the same as the last except using a high build primer and or finishing putty to fix the high lows on the flat sections between sanding.
If you are insistent on painting it yourself with your own gun make sure your compressor has sufficient capacity to keep up with your gun. And if you have any water coming through your lines you will need a drier.
Dust and dirt is a itchbay, getting a good clean room to do it in is vital. A ghetto garage trick to keeping dust and dirt from the floor from stirring up as you walk around is to hose down the floor first. The dust and dirt will get trapped in the water and should stay that way until the water dries up.
Above all else, prep work and patience is key.
Personally I think $200 is a pretty damn good deal around here.
