Good Split Testing Tool for 500,000+ Visitors A Month

I am looking for a good tool to split test 500,000+ visitors a month on our presell pages. However, the issue is most tools become unreasonable priced high at this amount of volume. I know there is Crazy Egg, but they can be expensive too. Anyone know of a good tool that can allow us to split test our pages, but also cross domain track the conversions?