Typically, we don't like questions regarding "cheapest" planning on the site - see a  very old debate here called [The WANTA™ debate (We are not travel agents)][1]. It's also documented in [our on-topic details page][2]:

> asking to have your travel itinerary constructed, including flight
> scheduling, budgeting and finding accommodation. Such questions cannot
> be answered as there are too many variables and personal preferences
> to account for, and are unlikely to be of use to others. An actual
> travel agent may be of assistance.

So a question about cheapest / best on a specific date or time period is off-topic as that's [a "shopping" question][3]. 

I do agree overall with [this comment from hippietrail above][4], which is a grey area where *some* "cheapest" questions are okay:

> I agree any question wanting current absolute cheapest ticket is not
> OK for the site. But questions wanting generally cheapest way or route
> is OK for the site. Especially when OPs do a decent job of explaining
> their criteria.

  [1]: https://travel.meta.stackexchange.com/q/1445/108
  [2]: http://travel.stackexchange.com/help/on-topic
  [3]: http://blog.stackoverflow.com/2010/11/qa-is-hard-lets-go-shopping/
  [4]: https://travel.meta.stackexchange.com/questions/3860/why-is-this-question-a-duplicate#comment11564_3860