I am a US citizen visiting Japan. I need a Chinese single-entry tourist visa. Is this possible?

Yes, you can apply for it at the Chines embassy or consulate in Japan. To apply for the single-entry L type, you should prepare your valid passport, a photocopy of the passport's data page, a filled application form affixed with your recently taken color photo, the original and photocopy of your entry permit for Japan, and round-trip tickets and hotel booking records.

Thanks for the reply! So I DO NOT need to get the Chinese entry permit through a travel agent in Japan? I can just go directly to the Embassy in Tokyo and apply for it myself as long as I have the correct paperwork? Also, I will not be staying at a hotel in China. I will be staying at a friend's home (this friend is currently living and working in China as an English teacher, but NOT a Chinese citizen) and hostels... How can I prove this when applying for my entry permit in Japan?

No, you don't need to apply for the entry permit through a travel agency and can directly apply for it by yourself. Since you have a friend in China, you are not required to submit the flight tickets and hotel reservations, an invitation letter from your friend will be enough for the application.

Is the invitation letter written on an official form or can it be any freehanded letter? What information needs to be included in it? And is it ok that the friend in China who would be writing the letter is NOT a Chinese national? He is a Ukranian citizen living and working China as an English teacher currently...

There is no fixed form for the invitation letter.

The letter should contain the following informtion:
(1) Information on you (full name, gender, date of birth, etc.)
(2) Information on the planned visit (arrival and departure dates, place(s) to be visited, etc.)
(3) Information on your friend (name, contact telephone number, address, signature)

It's OK even though your friend is not a Chinese citizen.

Perfect!! Also, I am traveling with a Canadian friend who also needs to get a single-entry Chinese tourist L type at the Embassy in Tokyo. He will be with me for the entirety of our stay in China (we will both be staying with our friend who lives in China). Can he also directly go to the Chinese Embassy in Tokyo w/ me and apply the same way I do? So he will not need confirmation of flights or hotel bookings as long as he has the same letter from our Chinese friend as I do?

Yes, his case is exactly the same with yours.

How much is the total cost for the visa (+ service fees) for me? And what is the cost for my Canadian friend?

Also, does the letter of invitation need to be sealed inside an envelope with a postage stamp from China? Or can he just email a scanned copy of it to us so we can print it out and bring them to the Embassy in Japan?

Also, how long will it take to process at the Chinese Embassy in Tokyo?

Regina, a scanned copy is ok in most cases. However, sometimes the embassy may require the original one.

It usually takes around four working days to deal with your application.

Americans need to pay JPY 15000 for four-day ordinary service. Your friend just needs to pay JPY 4000.