Safety is the most important thing, buy a Ferret50 or ALS upper. The two winningest 50 uppers made, best quality and best people to deal with.
ALS set the standard and Ferret50 is now the one all others want to be, call Dave and talk to him for a few minutes. You'll be giving him your CC info shortly after that and be happy for a short wait time. Buy once, cry once and forget that the second big price tag is the glass you'll need to make it hit what you want to distances out to 2000+ yards or more. Nightforce NXS series scopes are the number one scopes used, if you plan on shooting matches get the benchrest or for all around shooting get the standard NXS. The 5.5-22x56mm NXS will get you out to 2000 yards with a 30 or 50 MOA rail.
Don't forget to post some pics in the thread at the top of the page, got questions? Ask before you buy, there's plenty of guys here that have Ferrets and will help you out. Try to order as much stuff as you can on line to keep your costs down, you can actually see dollar signs roll up in people's eyes when you ask for 50 BMG stuff.
Be safe, have fun and enjoy whatever 50 upper you get.