Do you have an idea what they might offer?
Are they offering what you would make as an independent designer (contractor)?
If they are paying all your benefits (which is worth a few extra bucks an hour) I would not counter offer them with a higher wage. Your getting the extra $ in benefits.

However, if your expected to pay for your benefits and make an hourly wage that is not what a designer makes per hour, I would thank them for the offer but decline it and walk out. That would tell them know you know they have no clue what your worth.