Repairing an old tattoo(tattoo coverup)?

I was wondering what abouts were the prices , for working over an old piece of so called art. mistake when I was 14, 17 soon and im regretting it because it wasnt done profesionaly.(the guy said he had lots of experience, showed me a portfolio, all steralized and profesional on that side, he just failed my tattoo lol) anyways, its a small cross in black/blue maybe 2 1/2 inches by 2 inches, not large, on my shoulder, and i was wondering around how much it would cost to make a bigger tattoo over it, to completly cover it. are the rates same as when getting a new tat or more? thanks