I'm currently a student animator selling my soul in advertising; anyway, junior position wage in Australia for concept artist/animator is AUD $40,000 - 50,000.
I just did the maths and figured out the hourly rate of the workload.
If possibly try and get the pay in waves.
Like 1/4 at the beginning to seal the deal, another 1/4 midway and the rest of it at the end. Just what I've been told by friends in industry and it seems to go well. I've had issues with being paid in the past where it takes several weeks for the client to pay you.
Also, make sure you get a contract written up! It can be a nightmare!
Again, I'm fresh in the industry and am still learning the business side of it myself... My suggestion is look for what junior concept artist wage in your country is and then go from there.
Hopefully you'll get some replies from some members here who have more experience in the matter.
All the best.
Ever just woken up and gone "shit, does the world around me exist"?