I have had several over the years. The first 50 BMG rifle I purchased was an LAR Grizzly bullpup rifle. It was a great rifle to learn on. I ordered it with the match chamber so some surplus ammo would not chamber in it but that was of little concern to me as I only shot my own handloads using inspected pulled ball projectiles or the A-Max. With good loads, the rifle easily would hold moa at 1000 yards with my best three shot group measuring 5.566" ctc at 1K. That was with the 750 gr A-Max loaded to around 2630 fps.
The rifle was accurate, reliable and had a good trigger although not adjustable. Price wise, its hard to beat as they are right around $2000, one of the lower priced complete rifles but still very accurate. It is also very compact with its full 36" length barrel, its still MUCH shorter them most conventionally designed 30" barreled rifles.
The down side of this rifle is its slow to get into action for follow up shots if that is a concern because the bolt is integral with the recoil pad. Also, its not the most comfortable 50 BMG rifle to shoot. Currently they list the rifle at $2350 for the blued rifle. Here is a link to LAR.
largrizzly.com - Grizzly Big Boar
The second rifle I owned was a Barrett 82A1
As far as shear firepower, this is probably the most awsome rifle on the planet from a shear firepower and portability stand point. If you want to be able to hit a truck size target at 1000 yards, the Barrett 82 will certainly offer all the accuracy you want, If you want to shoot sub moa groups at 1000 yards, you will be challanged dramatically. Its design also limits what bullets can be used in the semi-auto mode, generally only ball or similiar shaped projectiles.
This is probably one of the funnest rifles I have ever shot but it was not as accurate as I wanted. It was very easy and comfortable to shoot as well. Bad thing is that your looking at $8000 for the currect retail price. They can be had for less then that but they are spendy, no way around that and for pure precision shooting, they will not satisfy you in the end that way, this is why that rifle is no longer with me. here is a link to Barrett, they also have a couple bolt action models as well which are more consistant on average and less expensive although they do not have the best triggers out there.
My current 50 cal rifle is the Armalite AR-50. This is the biggest of the three 50 cal rifles I have owned and its also the most comfortable to shoot with any load compared to the Barrett or LAR. It is also the loudest 50 BMG I have ever shot but thats because the brake is so efficent.
Cost wise, your looking at around $2600-$2700 depending on where you buy them. You can get aftermarket Rem 700 triggers that work great for precision trigger pulls and while the stocks are not all that pretty, they are set up well for rock solid shooting and are actually very comfortable with adjustable CP and butt plate.
I would call this rifle an upper end working rifle in fit and finish but it is what it is, a heavy single shot bolt rifle. They generally will easily hold moa out to 1000 yards and with preferred taylored loads they can be extremely accurate playing with the 1/2 moa range with some consistancy. My personal best three shot group at 1000 yards came with this rifle but after I fitted a new Lilja barrel to it chambered in my 510 Allen Magnum (50BMG Improved) which was a 3.987" ctc three shot group. That is by far my best group and that is not the norm but the rifle has that potential, I do not all the time.
AR-50 .50 BMG RIFLE
For the money, if you want a convetionally designed bolt action, the AR-50 is probably one of the best choices out there and for the money, they are hard to beat and extremely comfortable to shoot. My wife shoots my 510 AM with no problem at all.
Hope this helps some.