Remember in the donor tikka equation, you are also not necessarily buying bottom metal, a Wyatt box, or magazines. The factory bottom metal and plastic magazine is in fact lighter and tighter than most aftermarket options. Between those components and the trigger, a custom action has many hundreds of dollars to overcome. Then, you'll still be left with a hunting rifle that slam fires when it freezes, because all customs use rem 700 triggers.
I've come to the conclusion that Tikkas are for hunting and customs are for PRS. Of course, I shoot a Tikka for PRS anyway because I have so many donor actions lying around from buying them for bolts.
-J