Not able to finish items on kayne

Ive played kayn for two days straight now and when it comes to finish an item im not able to purchase it. Its not highlighted like i dont have the money to buy it when i have well over the amount i need and it will only be accessable at random points through the game. I played my last game and had to buy 3 BF swords because all i could do is buy items leading to a build.