I would second the Pierce, or any of the other actions mentioned for that matter and could name a few more. Like anything, if you want high quality, the price will likely match. That is not to say the more expensive $2500 action would necessarily be any better than say the $1500 Stiller.
If a guy was going to pick up an SPS just for the action, by the time the smoke clears he could easily have spent $1100-1500 on: The cost of the rifle, the cost of blueprinting, and the cost of adding features like side bolt release. In the end it would still be an R700 action.
For my cash, I would go with some sort of a custom, even if I had to save up a little more.