To make sure you have enough time to prepare, please apply the visa as early as you can. For most attendees, it is easier to apply for a Tourist ("L") visa; an invitation letter is NOT required for obtaining a Tourist visa.
When entering mainland China you’ll need a pre-arranged visa (unless you’re from Japan, Brunei, or Singapore) which you can arrange at a Chinese embassy or consulate anywhere in the world. The most commonly issued visa is an L (Tourist) Visa which is valid for a duration scaling from 30 days to one year for visitors. Prices are always fluctuating but expect to pay between $60-$130 depending on current rates and your nationality. Other types of visas include:
With the visa rules and regulations changing as often as they do, you’re best off contacting a Chinese consulate directly to make sure you’re getting totally accurate information. To give you an idea of the fluctuations, a year ago tourist visas weren’t being issued and now they’ve resumed operation including up to one-year duration.
For more information check the Chinese Embassy website in your country