What? If subtle clothing touches aren't enough to declare your Halo love... and, um, you've recently won the lottery... why not go whole hog and transform into Master Chief himself. Some studios will build you completely convincing armor for the right price. Or, be adventurous and construct it yourself.
Nightmare Armor Studios (buy it)
Mjolnir Armor Tutorials (build it)
How much? Nightmare charges between $2,000 and $5,000 for custom suits. Contact the company for details. Obviously, if you cobble together your own, the cost will depend on how much material, and how many mistakes, you commit along the way.