I own my own compresor. You have to figure in the cost of maintance from the manufactor or a service company. The cost of electric to run it. Oil for lub, and the cost of filters. I do nitrox so I have 4 filters, one regular and three hyper filters. I also have two water filters to keep the air dry. I also have a contract to have the air samples evaluated for quality.
I can fill about 20 tanks a day depending the working presure of the tank. The next ting you need is some kind of fill station. That can consist of 1 to 5 whips. Parts are very expensive and maintance is also very expensive. Anew compressor will cost you around $25,000.00 or more depending on what you get.
I hope this information will help you in making your decision.
Clay