我7月頭想到美國去, 約8月尾回, 想買平機票, 請問何時有美國機票優惠推廣

As this is a peak season (because the summer holiday) for air ticket, you better book your ticket after Easter. If you prefer an economic price ticket, you can consider for in-direct flight: such as Korean Airlines or Eva Airlines. Thus, you have to spend some time for the transit/ might need overnight stopover. Direct flight must expensive, especially for CX and SV.

Sometimes NW (Northwest) will do some ticket sells ad. on the newspaper. In addition, you better quote for few travelling agencies. Different travel agency would have different price. Even though might no much difference, as you are in tight budget, better save as much as you can. Also, find a good reputation one.

Enjoy your trip!

2007-01-14 14:40:42 補充：
In HK for air tix, the most expensive periods are: Chinese New Year, Easter, summer holiday, X'mas and New Year. Thus, the cheaper period is after Easter before holiday and after mid Sept to end of Oct. For the cheapest season is Nov - early Dec.

7 至9 月係全世界機票最貴既時候 12-3月最平 星期 1234 平 567 貴