You have to get in the habit of asking what the budget is for the job.
Don't be shy, or people will take advantage of you.
You have to have a price for what your hourly rate is otherwise you have no business taking work from anyone. Concept art ranges from 5 bucks an hour to a couple of hundred an hour and more. So it doesn't matter what any one else gets. If they want you they have a budget, you have a price- ask questions.
As for a contract most companies want exclusive rights to your work or work for hire so ask for the right to show it in your portfolio. Ask for their contract and NDA. Lay out how many rounds of changes are free after the initial pass is accepted. How often you get payed if it is a big job. I just finished two jobs that took about four months so I got paid every month. Create an invoice with your name, social or tax id number address
Keep track of your hours and bill with descriptions for the work
DATE: JULY 14, 2010
Big Megabuck Games
Final pass on Interface Buttons for main screen and view 55 hours
Additional Buttons and final pass on all requested interface artwork 12 hours
Additional assets and fixes on main view rooms 93 hours
@ XX per Hour
Make all checks payable to Your Name
Payment is due within 30 days.
If you have any questions concerning this invoice, contact your name your phone
Thank you for your business!