$10 pads are worth it in my opinion. At the $300 point? Well you can wait and find HD650's around $330 and up. You can get the a900x for about $180 at Best Buy right now. I won't say the a900x is better because I'm going from memory but when my new pair arrive I'll be able to A/B them to my hearts content.
Are you ok with trying them from Amazon? There is no restocking fee so you have nothing to lose but I know some people don't want the hassle of returning anything. I don't think you can go terribly 'wrong' with the HE-400.
One thing though, what amp?