ajnaro,

There is no single source anymore. ExpertFlyer is probably the best one.

In the last few years a number of the cheapest points including Sri Lanka, Pakistan, South Africa and Sudan have increased substantially, I suspect in part due to publication on this forum.

But it is all relative. The cheapest xONEx is a combination of
- the cost of the xONEx, your cost to get there, restrictions introduced by starting point (eg country of origin) based on your routing, the cost and difficulty in making the booking.