The Many-Colored Land by Julian May is $1.99 at amazon.com and barnes and noble.
http://www.amazon.com/Many-Colored-L...dp/B00633YOUU/
When a one-way time tunnel to Earth's distant past, specifically six million B.C., was discovered by folks on the Galactic Milieu, every misfit for light-years around hurried to pass through it. Each sought his own brand of happiness. But none could have guessed what awaited them. Not even in a million years....
THE SAGA OF PLIOCENE EXILE
Volume I:THE MANY-COLORED LAND
Volume II:THE GOLDEN TORC
Volume III:THE NONBORN KING
Volume IV:THE ADVERSARY