If you still need to purchase a receiver, I would strongly recommend either the Defiance Machining Rebel or the Borden Timberline Magnum. You can get into both of these receivers for around $1000.
Once you figure the price you would have into a Rem 700, especially if you wanted a stainless receiver, then add on fully accurizing the reciever and properly modifing it to get it ready to build a precision rifle on, you can easily have +$1000 into the receiver and machining with a Rem 700.
Plus in the end, you still have a Rem 700 which is not a bad thing but nothing close to the quality and strength of these other two receivers.
The two custom receivers can be orders with extended magazine box windows for drop in fit for custom mag boxes for extra length for your ammo with long range match bullets.
Also, in the end, a rifle built on a full custom receiver will retain more resell value then any modified factory rifle. Not saying you will be selling the rifle down the road but if you do a rifle using a top quality custom receiver will bring more money then a modified factory rifle.
Now, if you just are going to screw on a barrel to a receiver and go, it does not make alot of difference so it depends on what type of rifle build you are planning. In my opinion, for a top quality precision rifle, there is no question that the custom receivers are the best investment buck as they cost very little if any more then a fully machined and prepped factory receiver would these days.