What is the cheapest/easiest way to get stat-boosting items in X?

Question

I find that super training requires a lot of focus, so where can I find Proteins, HP Ups, etc., for the cheapest price?

Answer 1

You can buy all of the EV items in the Lavarre city Pokemon Center (Poke Mart) for 9800 each.
The only way to make it cheaper is to use Bargain O-Power III, that would make each cost 4900.

Or you can buy them at the Battle Maison for 2BP each.

Source - Bulbapedia.
Hope I helped!

Answer 2

The battle maison each drink is only 2 battle points doing the battle test gives you at enough for at least 5 drinks you could also battle in the maison for 1-2 each (regular) or 2-7 (super) or you can buy them in Laverre city with bargain power 3 for 4,900 each

Answer 3

If you have a lot of BP, you could go to the Battle Maison and buy all of the Vitamins(Protein, Carbos, etc.) for 2 bp! So you can save your money AND use a little bit of your BP! It's a win-win! Hope I helped!
Source: Experience

Answer 4

In southern lumiose city, in the Pokemon man center that sells stuff like PP Hups, and rare candys, and I think he may have the vitamins to boost stat, but all of the cost of BP. The easiest way ever to get BP is to wonder trade, you get about 25-50 BP points every time you wonder trade. So basically by doing this, you can get unlimited vitamins and rare candys. Hope this helped you out!