How much should I have to apply for a China visa?

It should be equal to USD100 per day.

OK 100 DOLLARS PER DAY,IF I TAKE 800 DOLLARS IN TRAVELER CHEQUES,CAN I STAY ONE WEEK FOR HOLIDAY

Once you obtain the visa, nobody cares how much you take into China only if it doesn't break China law.
But I'm afraid you won't successfully get the visa if you only have USD800 even if you'll only stay in China for 7 days. Because there is no such kind of China visa with a duration of stay for 7 days. The duration of stay is usually 30 days for a single-entry visa.
BTW, the embassy has never told the minimum amount of money for the applicant to present while applying for the visa. Also, travel cheque is not so popular in China, so it maybe inconvenient to use it within China.

THANK YOU DAVID AS YOU SEEM TO KNOW A LOT,IF I JUST SHOW MY BANK ACCOUNT AND WHAT MONEY DO I NEED TO SPEND IN CHINA,CAN I TAKE THAI MONEY AND CHANGE IT OR US DOLLARS ONLY WANTED TO HAVE A HOLIDAY

You can show your bank account with adequate money for China visa, once you get a China visa, you can take Thai money and change it in China or take US dollar.