I wasn’t too specific when explaining some EV stuff earlier, but this should make EV training the easiest ever. First, I already explained the 252 principle, which is to keep count of EVs until you get to 252 in one stat. Since a Pokemon will have 510 EVs total, it will have 6 left over if you decide to completely EV train for two stats. However, you will only get to increase the leftover stat by 1, since there is a “mathfloor” function. This means that even though you have 3 EVs in one stat, it will not round up, but down to the nearest number.
I forgot to mention the “Power” items, which can be found in the Battle Subway for 16 BP. Each item gives extra EVs for a certain stat, and it comes in all stats, including HP. What these power items do is add 4 EVs of that stat to the EVs you get from regular EV training. For example, a Litwick gives one EV for Special Attack. If you have the Power Lens, which increases Special Attack EVs, you will get four. This means that you will only need to defeat 32 (30 with the item, and 2 without) to get that stat EV trained.
If you have the money, I recommend you spend it on Vitamins. You might be thinking that the formula I have up there equals 152. This is because I’ve assumed that you gave your Pokémon Vitamins, which power up their EVs before the training even starts. Like I said before, it can go up to a maximum of 100, which is 10 Vitamins. In total, you will need 196,000 Poke Dollars to EV train a Pokemon. You need 20 Vitamins for 200 EVs, which will cost 9,800 Poke Dollars each. Multiply 20, and you will fall a little short of 200,000 Poke Dollars. To get this intimidating amount, you can fight athletes in Nimbasa City with the Amulet Coin/Luck Incense and get quite a bit of money.
Since I haven’t been EV training, what with all this writing, I have saved up 1.8 million Poke Dollars. That means I can EV train 9 Pokemon of my choice whenever I find a Pokemon that I like. For HP EVs, try looking for Audino or Alomomola in the shaking spots. For Attack, Lillipup and Patrat in Route 1 will keep you from overlevelling your Pokemon. For Defense, try searching for Venipede or Sewaddle in Pinwheel Forest. Celestial Tower has a 100% Litwick/Elgyem rate for Special Attack. For Special Defense, fight Frillish by surfing east of Driftveil City. Finally, for Speed, Basculin in the water by Route 1 will give two Speed EVs. With the right amount of time and money (the latter is optional), you can instantly create Pokemon with better potential in the stats you want. Depending on your Pokemon, you can make a good strategy, but most of all, remember to have fun, and don’t lose track of your EVs. If you do, go to the house north of the Pokemon Center in Opelucid City. A girl will tell you if you’ve fully EV trained your Pokemon.