Hi there!
I'm Nico, an experienced artist in both digital and traditional art techniques and any artstyle from realistic to cartoonish. I've made cover arts for books and music albums, posters, clothing designs, concept art for videogames, website backgrounds, etc.
About how much it could be, it depends on a lot of things: the artstyle, te level of polishment, the backgrounds, etc. For an artstyle and quality like for example Hearthstone, it could take from 3 to 5 hours per card, so 30$ to 50$ per card could be an aproximated price. Then the boards and box could take a bit longer. But, if you are looking for something more realistic like Magic the Gathering, it could take up to 10 hours per card, so 50$ for it starts to be a bit unfair.
The best way to work around something that unpredictable is to agree on an hourly price. So, to make sure that you feel comfortable with that, we could agree on a limit price per card. That way I'll make sure to not exceed it and if it takes less than that limit we agreed per card, it's money you save!
About my professional qualities, I'm really perfectionist and like to do my images as perfect and close as possible to the client's demand. I'm constantly asking about the details of the project, showing the work in progress and working hard to finish on time without losing quality.
I have most of my artworks posted on my portfolio in freelancer.com, but I can send you a PDF if you need it!
Looking forward to hear from you! Nico