Flute

YAMAHA YFL 212

(RECOMMENDED)

Current Street Price with an Educational Discount: $ 799
Yamaha's student flute with a "Split E".
I'm not a woodwind expert, so for further recommendations or information please consult a flute expert. (Note: By Expert, I do not mean just someone who plays it, or even someone who teaches it. I mean someone who knows the makes and models, how well they last, the pros and cons and what their likely resale value is second hand. Be very careful of reviews on the internet unless you can verify the writer is truly an unbiased expert. You will find lots of glowing reviews of instruments that aren't even worth the cost of the freight)
I wouldn't recommend a cheaper flute than this model as the quality is just not there. 
This model will usually resell in good condition, fully serviced for $ 400 - 500+ making it a very affordable cost of ownership.
The flute experts I have consulted all recommend getting the "split E" key.

Intermediate Flutes

For parents looking to buy a flute which will last right through high school, an Intermediate flute can be a great investment.
Again, I'd recommend talking to a flute expert who can give you detailed advice. Brands with good intermediate offerings which seem to be popular and are widely available include: Yamaha and Pearl

second hand

Please read my guide to buying second hand.
Fully serviced and from a reputable second hand source, in great condition, you can expect to pay around:

Yamaha  YFL-211 $ 510
Pearl PF505 (or 501) $ 510