3000x4000 is probably close. I'm guessing that's close to 300DPI at size? If so, I would say it's good enough IF the photoshop file doesn't look like it's losing data compared to the real thing. The main issue might be dealing with stochastic dots if those were used in the original art. If it's pretty smooth and the dots are small, fixing it up in Photoshop and then having someone output should be no big deal.
As for pricing, when I do this stuff professionally, I charge a lot. Here on the arcade boards I charge a fraction, or trade if possible. Last time I did something for someone here it was about 6 hours of work and I think I ended up being paid about $20 an hour. It was pretty complicated stuff... had to airbrush out a lot of stuff. I attached a before and after just so you can see .