I need a vector designer (for casual games)

Information on the business: We offer free games online
Industry: Entertainment
Design details: We need 5 vector backgrounds (900x500) for a 2D game. Prehistorical theme.
It's a "flying along" game. Game style is cartoon. Arcade game. For all audience.

Backgrounds must be able to be repeated in displaying. This is for a "endless" game.
Each background is corresponding to a level in game.
From 1st background (1st level) to 5th background (5th level). Progressively more "dark", more "harder" theme.

Don't hesitate to answer me if you have any question.
Target audience: Casual players/for all audience
Ideas for the visual style: Cartoon/casual/rounded/sweet/happy
Things to avoid: Theme need to stay happy (not horror style)
Where the design will be used: For a free web game
Extra notes:
Angry Birds design is a perfect example of what we want to approach in quality.