Not sure what one of the custom actions sells for, but I have been impressed by the quaility and tolerances in the MK V Weatherby actions. You can usually find a donor rifle for less than $800 if you look. They have a magazine box that avg's 3.8" inside length, and lends itself to shaping the lips for good feeding instead of having to work the receiver rails. They have a good trigger design that can be tuned to a clean, crisp let-off. Also, the bolt faces are a breeze to open up. Be sure they are the 9 lug, though.
H.P. White Laboratories pressure tested them several years ago and I believe that they finally quit when brass extruded into the locking lugs and the bolt could not be hammered open. Don't quote me on that, but I do remember that they were incredibly strong.
Custom stocks are available for these actions. I like Accurate Innovations stocks in wood or laminate. They are available with up to Shilen #8 taper barrel channels. They all come with an aluminum chassis and pillar blocks installed.
Whatever you decide, enjoy; Tom