Typically, an invitation to China can be obtained free of charge, If you make an agreement with the Chinese company about his visit. Also, you will be sent an invitation to a free contract (for your work), to conference, You can get it in the mail to attend the exhibition (eg, Кантонской ярмарки). If you go to an intermediary company, you offer full service visa, for which you will make the invitation and. The cost of these services varies from the desired length of stay and the firm.