TECHNOLOGY FOR ETIs MORE EXPENSIVE AT OPTICAL WAVELENGTHS
Optical and laser technology is inherently more complicated and expensive than its microwave counterpart, and since optical photons are more energetic than "warm fuzzy" microwave photons, economic considerations would dictate the use of the lower-cost microwave system.
It is always dubious to make economic comparisons between technologies, which in late 20th Century earth are such that one is mature and the other has a long way to go yet.
There is no doubt that if we tried to field a high-power space-based laser transmitter system today, the cost would be extremely high, notwithstanding the fact that we don't yet have the knowledge-base and capability to do the required point-ahead targeting. However, for ETIs this would be trivial, and the reason for choosing a particular technology for contacting other civilizations would not be governed by our present-day economics. Remember, the ETIs will be able to target very narrow beams, so the energy cost per optical photon landed on the target will most likely be a lot less than the energy cost to land a microwave photon! This is notwithstanding the fact that the former photons require more energy to be generated.
How can we compare the cost of a PC with an abacus? By early next century, the cost of manufacturing a PC, far more powerful than today's Pentiums, will be more than the cost to manufacture an abacus. On grounds of today's economics, one would say that if one just wanted to add up some numbers, it would be foolish to pay extra for a PC. But next century, the economics could be very different!