Some persons argue ET will use 1.42 GHz for their transmissions. Maybee they will, maybee they won't.

Would it be possible to make an agreement where to beam a signal and thereby where to listen for one?

Most ETs live in a narrow band in the sky, the galactic plane. Their distribution is similar to the distribution of pulsars in the Einstein@home screensaver (If you are running that as well). ET will also realise this and direct most of their transmissions towards the galactic plane. So searching anything but the galactic plane would be double futile.

Is it possible to reduce the cost of trasmission and searching further? Could we agree on what ET planet to peer with?

To do this we would need a common reference point. Could we use the galaxy center?

The transmitting end probably do not have enuf money to transmit messages, for many thousand years, to all other ETs in the galaxy. If the transmitting end limits their transmissions to a (set of)beam(s) covering aproximatly one moondiameter around the galaxy center, powerfull enuf to be detected on the other side of the galaxy, they would save a lot of money and they could still be pretty shure someone intecepts their signal. (the cost per star is inverse proportional to the length of the beam) .

The receiving could study aproximatly one moondiameter around the galaxy center searching for a signal from ET. Limiting the search area would reduce the cost for the receiving end and increase the chance of a detection.

Would this create a least cost link?

How freqently could we expect a signal, and what would the duration of a signel be?