All of the options offered by Puertoricarious are viable and will work for you but I have found that later on the process when you're looking at 60k cp for the least expensive skills, Adamantortoise / Adamantoise farming is the way to go. There is a very easy method that will allow you to kill them without having to use shrouds or a summon (which can become costly after a while).
1. It goes without saying that by the time you're able to take on Adamantortoises, you should have acquired the Growth Egg to allow you get double CP for every encounter. Set up your paradigm deck like so: Cerberus (3 Com), Tri-Disaster (3 Rav), Infiltration (3 Sab), Rapid Growth (3 Syn), and Salvation (3 Med) for Fang, Hope, and Lightning. It's not necessary to have each person all the way leveled up in each of those classes you're just going for speed in each phase of the fight.
2. Have Genji Gloves (if you've got them) on Lightning and Fang and set your Rapid Growth paradigm as the default. I also had an Energy Sash on Fang and Collector's and Connosieur's Catelogs on Hope. The rest of my accessories are strength and magic stat boosts. Finally, make Fang party leader.
3. Make the pull and begin by buffing everyone with Haste, Protection, Bravery, and Faith. Shell will help if he manages to get off a Quake but is not essential. Once everyone is buffed top off your hp with Salvation and switch to Infiltration to debuff one of the legs. Deshell, Deprotect, and Imperil are all you really need. Odds are the leg is already staggered from being debuffed but if it is not, quickly go into Tri-disaster to get it there and finally go to town with Cerberus. Once the leg is at about 70% hp, you should be able to use Fang's Highwind attack to kill it the rest of the way in one action. Heal up if you need to and repeat on the other leg. Once you're buffed, taking out the two legs should only take you about 40 sec or less.
4. As he starts to fall, switch to infiltration once again and inflict him with Deshell, Slow, Deprotect, and Imperil. Now quickly switch to Tri-Disaster and bring the stagger meter to a minimum of 750% or so (more is better but time is a factor so use your judgement). Then switch to Cerberus and his health will just melt away. This is where the Genji Gloves become essential on at least Fang. In my game when I switch to Cerberus, her first attacks are dealing more than 120k damage. It should die quickly without being able to get back up.
This tactic seems as though it might take more time than a summon but once you get a rhythm down you should be able to kill one in about 2-2.5 min and get 80k cp as well as a fair number of Platinum Ingots and a few Trapezohedrons. The strategy also works well for the Adamantoises you just may need to heal one or two more times before you bring him down.
Because you're not relying on summons, you will have TP available to use one if something goes wrong. Should that happen, the Energy Sash refills a large portion of the meter with every Adamantortoise kill and as long as you don't rely on it too heavily, you shouldn't have to farm TP points at all. If you find you have to use summons more often than I did, you can try also equipping a Champion's Badge. Once all 4 Oretortoises (or 5 if Mark 63 is active) are dead, save your game and reload the save to respawn them. You'll get the CP you need in no time and you have the added benefit of cash from the ingots and catalysts to craft your ultimate weapons.
I find this method works better for me than spamming Death with Vanille as it is 100% consistant once you get the required rhythm down. As a side note, there is one Adamantortoise that has 3 lowlevel dog/wolf/skag things running around in front of it. The strategy for that fight is exactly the same, just open with Cerberus and spam Blitz and they should die in 2-3 seconds. After that, continue as normal.
*EDIT*- A Genji Glove is more or less essential if you want Fang's Highwind attack to be effective (without it it will cap the attack's damage at 99,999). With the accessory it will easily do over 300-400k damage on a staggered leg.
As per Seraphim Needed's suggestion, I'll outline where to get Genji Gloves and the Growth Egg.
The Growth Egg is acquired for completing Mark Mission 55 (Cant We All Just Get Along?) by killing a Neochu. Without going into too much detail, this is easiest done by spamming Death with Vanille. Puertoricarious has a good method for accomplishing this in the guide above.
Genji Gloves can be acquired in 3 different places: Mark Mission 51 (Attacus, The Soulless), Mark Mission 62 (Indomitable Will), and Mark Mission 63 (Crushed By Doubt)