If you're planning to focus working in oils and acrylic, then you're probably better off not investing in the Copics. (although they are brilliant for doing colour roughs!) Each marker is $8(AUS) and the refills are $11 each.
The main reason I reccommend not is that the markers are a transparent medium, like watercolour, and have to be applied lightest colour to darkest. Whereas oils and acrylics are opaque mediums, and are generally applied dark to light. So the application method is quite opposite. ;~)