Forget the Sig .50, its a Tac-50 with Sig's name on it and a couple grand added to the price.
Take a look at the EDM Arms M96 Windrunner, its more then the Tac-50 but just as accurate. Plus you can break it down into a 30" package, easy to store and move. If you want great accuracy that won't break the bank, look at State Arms/Eastridge Guns. Slap a Nightforce NXS 5.5-22X56mm and you'll be hitting 1000 yards all day long with ease.
If you're still budget minded look at the AR-50 in standard or National Match version. The AR-50 is probably the most popular .50 BMG off the shelf rifle and probably out sells all others 2 to 1.
I see the world thru bloodshot eyes
Streets filled with blood from distant lies
The dogs of war never compromise,
No time for rearranging.