Unlike the other bids here, I'm going to make you an offer that is within your projects budget.
However given that the budget is low, there really is a limit to what I can do for you which I'll state as clearly as I can.
I won't export to iOS. I will however develop the project in a way that makes doing so easy, should you wish to hire someone else to do so afterwards.
The game will however be testable using Windows and Mac, as Unity allows for exporting the same game to many platforms easily.
As for the game itself, at the very least I can provide a racing game with a few stages, opponents and some other basic functionality. (If you have specific ideas and mechanics in mind we can discuss them).
For the graphics,
If it's a 3D game, I won't be creating any more than minimalistic shapes for the environment, however, with the use of good lighting and effects, these can still result in a game that looks great.
If the game is 2D, I'm afraid I won't be much use when it comes to graphics as I'm primarily a programmer and game designer, not an artist.
However, there are many free assets that do exist and can be used in your game.
It's also worth noting, that assets can always be switched out quite easily at a later point should you wish to do so.
I know that's probably not what you were hoping for, but given your proposed budget, I think I'm making you a very good offer.
Feel free to contact me if you'd like to discuss things first.