That is a bit of an exaggeration. A fully upgraded RPR is about $2000. Full in-house Surgeon builds are around $6k (not that I would ever choose surgeon to build me a rifle). A custom rifle from any of the top builders in the U.S. will start at around $4k (U.S. dollars of course) and go up from there.
So a fully decked out RPR with custom barrel, etc. will still be half to a third of the price of a full blown custom, and most likely shoot just as well if not damn near to it. The quality of a custom rifle will still be better (fit, finish, etc.), and with a custom you can get a rifle built exactly the way you want. But a PRS capable rifle at $1-2K is a pretty good bargain. If you are already eyeing up full built custom rifles, you were never looking at purchasing an RPR anyways. An RPR is not designed to compete with those rifles, but to be a cheaper alternative for people wanting to get into the PRS game, and still be competitive.
A more realistic alternative to a fully decked out RPR is a Tikka (such as a CTR) thrown into a KRG Whiskey-3 chassis. For around the same price, you have another fairly competitive rifle, in a higher quality chassis. An aftermarket barrel however will probably shoot you over the price of a fully decked out RPR, but is worth considering.
A good savage will do the same. Trued remington 700 action, Tikka, etc. In all fairness, a cheap action matched well with an excellent barrel, will produce a quality shooter, and match grade loads of course. But the reason people buy a quality action is that, well, they are always dependable. A one piece action like a surgeon for eg, with the integral recoil lug and pic rail, will last longer than any barrel. You could run the thing through multiple barrels and pass it down to your great grandkids. An action with a lot of small pieces, like a savage, well, it's cheaper to buy a new one. They still shoot the same when new, but over time, the small pieces wear; whereas the one piece of machined steel still shines.
What does that time frame look like? I don't know. Could be 1,000,000 rounds before the savage action wears. Could be longer, could be shorter. But that's where confidence comes in: a surgeon type action is very durable. It's one piece of steel. Do I feel more confident shooting one solid piece of steel? Yes, I do. And then resale reflects that durability. Custom rifles, it is argued, go for less than a quality build, like a pgw for example. But, from what I've seen, surgeons or defiance and etc, do not when compared to a quality barrel screwed on to a cheap action (trued, savage, etc). Surgeon's hold their value. Who the gunsmith is plays a part, as it should. But, all that a gunsmith does, with a quality made action, is reamer and screw on the barrel. With a remington, the smith has to true the action and etc, which adds to the 'nebulous' realm and brings down value.
Anyway, with the cheap guns, like ruger pr, savage, tikka, etc, putting money into them, if they come with a solid stock and etc, does not make sense. Well, unless you do not want to sell at any point. There are too many variables that cast doubt on the sale price. Screw on a quality barrel and yes, you have a shooter. But decide to move on to something else, and maybe you'll lose an acceptable depreciation-like amount, or maybe more. Or maybe none at all, maybe you'll make money. Who knows. But, the question is, are you willing to take the risk?
Anyway, just my 2 cents, for what it's worth