Cheapest Flights - how??

There has to be a good way to do this...

I want to search for the cheapest flights to get approximately 3-4 weeks in Karachi, Pakistan some time between mid November 2013 and the end of February 2014 for a university student. This is so my flatmate can go home for a while when university is out.

She's happy to vary basically anything for cheaper flight cost: annoying transfers, early payment, uncommon airlines, different days, different time away, etc.

I'm willing to spend the time to set up notifications and track search results or whatever if it'd help me find the best fare - I just don't know how. I've never booked international tickets before!! Actually I won't be booking these but my flatmate is busy studying so she doesn't have time to mess around looking, so I'm doing that part.

Initial searches say it'll be about $1,500 return. Are there sites where I can say "email me if this search result turns up under $1300" or something equivalent?

Also I'm not sure when's best to search for such a wide range of dates - Just using common sense I'm guessing that February will be best but the actual sites I found only let me search +/- 3 days.

Suggestions and hints welcome!

ETA: I'm in Melbourne, Australia. I can't believe I forgot to add that ...