A proper glossy finish takes time to achieve. It requires lots of sanding and filling to make sure the surface is absolutely smooth, painting, sanding, painting again, sanding again, painting again, wet sanding, clearcoating, wet sanding, clear coating again, and then a final polish. Pretty enclosures take time, cost money and are not cheap. Bulding yourself would be the most economical.
Parts for the actual enclosure usually run about $40-$50 if you have all of the tools necessary.
Materials for finishing an enclosure (to a proper glossy/mirror finish) will be at least that & probably more depending upon the type of paint used. The time is the biggest part. High quality finishes cannot be rushed. They need to be applied properly too with a good sprayer & wet sander.