Game sprite sheet

Hi, I am returning to game development and so I am starting with a very basic game, which is a remake of space invaders. ? I am likely to give this project away free of charge and so I require custom graphics that are not covered by anyone's IP. I am looking for an experienced game artist that will create a sprite sheet(s) for the game. ? They have to look very professional and be structured correctly. ? I am looking for a spaceship, barrier, ufo, some aliens of differing types, some weapons and some projectiles (bullet, missile, etc). I will pay you for the graphics and depending on your input I would consider giving you credits within the game itself. As I said this is likely to be an open source product in the end and so please consider that when bidding. ? Bidders with examples of their work would be considered before ones without.