How can i get from mexico city to oaxaca on bus, and how much will it be?

help fast

can you give me the web site, and if any in english

It takes approximately 6 hours and it cost about $40 USD each way. You can actually book the ticket in the enclosed site. Just remember prices are in Mexican pesos which are about $10 pesos per dollar.

I have always travelled via ADO in Mexico. Here is their website http://www.ado.com.mx/

I did it last summer. It takes about 6-8 hours on bus. Metro to San Lazaro to TAPO, the First Class Station Terminal and book a ticket. You can book a ticket by showing up. There's several trips a day, but it may be best to look online or do what we did which was go there the day before we went to Oaxaca and book our ticket.

If you go directly to Oaxaca city you have to go to TAPO the bus station of the East. If you go to the beaches of Oaxaca you have to go to Tasquena, the bus station of the south.
You can travel by UNO,ADO or Cristobal Colon, they are the same company but with different service UNO is the most expensive cos it has much more space between seats, the seats go really down and back to sleep very comfortable and they have cafeteria outside and inside the bus, the waiting rooms are really quiet and private, it has earphones for the TV and radio it costs more or less 40 USD, ADO GL (30USD) and normal ADO is first class stuff, in my opinion the difference is not too much from normal ADO sometimes has better buses than the GL only if you are extremely tall as my boyfriend you can notice the difference in the space, he is 1.96 m I am only 1.60 so I do not notice it, Cristobal Colon is the cheapest but are good buses as well, they are first class not deluxe I think they dont have TV ah and they dont have toilet on board I think, but the seats are as good as the other ones the space exactly the same than normal ADO. It cost around 26 USD.
To book or see schedules go to ticketbus.com.mx and buy lonelyplanet Mexico its a good guide, I am mexican and even that I have mine to travel.