The price of tattoo supplies varies depending on the quality of the equipment and the supplier. The power supplies will cost in the range of $150-$300, but you can find tattoo power supplies on eBay or Amazon for $80-$100. Remember though when buying anything including tattoo supplies, you get what you pay for.
Tattoo machines are also a very important part of your tattoo supplies; they can also be brought on eBay, but it's best to shop around online before you make that final decision. If you go for a better or more expensive tattoo machine it will last you a lifetime and you will more than get your money back; they will pay for them self really quickly.
The clip cord and pedal are usually an additional $40; sometimes you can find them a lot cheaper if you look around. The tattoo tubes also vary a lot in price; you can buy disposable tattoo tubes for under $1, but you are not going to have as much control over your machine. Tattoo caps can be brought for around $20 by the thousand depending on the size.
Tattoo inks can be brought very cheaply but you are better off using some of the better more expensive tattoo inks. You can expect to pay around $30 for an 8 oz bottle of colored tattoo ink, depending on the color.