I've built cabinets mainly for EM pins. They are not that difficult to build, after you have done a few. For the material I use pure birch 3/4" plywood, runs around $48 - 60 per sheet depend where you buy it, and how many sheet you purchase. I can get the bottom cabinet and back box cabinet out of a single sheet. For the backbox trim and corner bracing I buy clear birch. This is a good material for painting, done right you get a nice smooth finish, I only provide a smooth finished cabinet, the buyer has to provide his own final paint or decals. For the bottom board of the cabinet I use pure birch 1/2" plywood.

If you are going to charge by the hour for your time the cost of building one cabinet will seem to be high. If you charge per cabinet, and are not too concerned about making a full time wage, this is a good part time business. I could produce one finished cabinet per week.

My background has been in carpentry for 40 years, so I had all the equipment and suppliers available to me. If you are just starting out, I would recommend a good panel saw for plywood material cutting, beats a table saw any day, a HVLP paint system. Hope this helps you a little.