I would like to know how long it takes to get the visa?

It usually takes four working days. However, you are suggested to apply for it one month in advance in case you are refused and your trip/business is affected.

hello dear i am from mexico and Iwould like to know how much it is cost for it?

and I would like to know how long it takes to get?

Because I like to travel in a month. next jun 28 to29 I will go to apply next thursday then when i should back for it.

Fee is 35,000 won for a single entry, but as what the embassy requires, you need to apply through a local travel agency. So, you need to pay extra fee for their service. Generally, it takes 4 working days. If you submit application on Thursday, you can collect it on following Wednesday.