You did not mention if you are an experienced ammo loader or shooter.
I have given up shooting Target Rifle and switched over to F Class. I find F Class different, more relaxed and more fun. TR is what I used to take quite seriously.
You can often find a used 308 target rifle (a real one, as used in DCRA type competition) for about $600 to $1,000. That is probably less than the cost of the action. Put a scope on the rifle and you can do a lot of shooting and learning.
As for 6.5-284, I have burned out 3 barrels already in that caliber. Get about 2,000 roudns out of it. Some guys get terrific short range accuracy out of their but I never did. Would not hold the V bull at 500 yards for me.
Along the way I aquired a CIL 950T (Savage) with a new hart barrel in 6.5x55. I bought it from Paul Reibin for $450. (The original owner must have paid more than that for the barrel and chambering.) I intended to re-chamber it to 6.5x284, but tried it out first. It shot like a house on fire. I lent it to a friend who took it to Bisley to shoot the Millenium F Class Championships. he shot quite a few possibles.
It got left in that caliber and shot out at about 3,000 rounds. It had a 30" barrel and this got me thinking that maybe I don't need a 6.5-284 for the velocity. It was only about 100 fps slower than my wife's 28" 6.5-284.
So I rebarreled all our 6.5-284s over to 6.5-08 Ackley. With Winchester 308 brass sized in a 260 Rem FL die, we fire form the brass with a Sierra 140 Match bullet on top of 45 to 46 gr of IMR4350. About 2800 fps. At short ranges this ammo holds the V bull easily.
The formed brass is shot with the same bullet on top of 50 to 51 gr of RL22. OAL is 2.925 (chamber is deep so bullet can be seated long.) Velocity runs between 2925 and 3000 fps. (Each rifle is different, and the wife's has a 32" barrel.)
These loads work well in my barrels (McLennan) chambered with my chamber design (available from JGS). They are probably hot and at least 5 grains over where a load test should start.
If a Remington or Lapua case is used, my load is 1 or 2 grains less.
From what I have seen so far, the case capacity of the Winchester case is identical to the 6.5x55. Just shorter and fatter. Velocity is about the same as what most 6.5-284 shooters use as an accuracy load, so we don't give up anything at long range.
It looks like short range accuracy is better, even with the case forming loads, and I expect barrel life to be longer than teh 6.5x284.
Barrel life of a blue 308 is in the order of 2,000 rounds. A stainless 308 is about double that. Some have lasted much longer.
If you new at loading, I suggest you buy a 308 and get some expereince. By the time you burn the barrel out ( a year or two) you can consider a 6.5.
If you are an experienced loader, then running 308 (or 7-08 cases through a 260 die is no big deal. I doubt that components are an issue. I buy bullets by the 1,000 bullet box and have never had any trouble locating more when I need them.
Each of our rifles has its own dedicated batch of brass - 500 pieces each. That seems to be enough. I scrap the brass when I scrap the barrel. new brass is weighed and sorted in .5 grain batches and loaded into 50 round boxes. Bullets are bought a few thousand for each rifel at a time, and primers in cases of 5000. This way there is no change in components over the course of the barrel.
308 is a bit more forgiving to load than 6.5, so keeping components a constant lot number is a good idea. The long bearing surface of the 6.5 bullet measn things can get out of hand quickly if the load is too hot, or, say, becomes too hot because it is a hot day.
I saw a very badly blown primer form the first shot in a rifle loaded with the Starting load in the book. Same ammo was quite mild in another 6.5x55.
If you opt for a 6.5, I suggest you consider starting with a 260 Rem Ackley (same as a 6.5-08 Ackley).