I have rebuild a couple of engines (couple of Renault, and a 2.3-16 MB)that are stille running well!), and I can say that the most expensive parts are the pistons.

Mostly, the bearings are very cheap, here in the Netherlands MB bearings were CHEAPER and faster delivered than aftermaket ones.
Expect max. 200-300 euros for bearings and oil simmer rings.
Oil pump ussually is not very expensive either (100 euros).

pistons for a turbodiesel are here available for 130-140 euros a piece, and 200 for a 'kitset' (i think this is with liner). Mahle brand, which is good. (I am talking aftermarket here, maybe MB is cheaper, you never know....)

Then you need the timing chain, sprockets, gaskets etc.

But again: in the engine you'll lose the most on pistons.

When the engine is still runing good, you only have to get the crank measured, and maybe polish it a bit, and its ok.
I dont think its doable if you have 2 left hands. I myself am a mechanic and specialised in man. gearbox overhauling (and a bit experience with overhauling engines), and have a workshop with most the tools (not the big machinery for boring out cilinders etc.), so i can do it in a couple of days.
But if you are a newbie to this, you'll:
-have to invest a couple of hundred in tools
-have to have a couple of weeks time
-have to go for several jobs to a overhauling company (like myself) for the expensive-machinery-work

In the end youll be saving a couple of grand i think.

Then a few remarks:
-what are shortblocks (and are there also tall blocks?) and what are the differences
-I thought because the 603 is a iron cast block, you dont need liners, just oversized pistons. ( a nephew of my woman is the main man for boring and honing cilinders at the company where i worked, I also can ask him why)