On p.38 of this presentation, there’s a breakdown of the contributions to the cost of Space Solar Power (SSP). Not surprisingly, the installation is more than half of the cost and another 20% is manufacturing cost of the solar array.
If we extract out the solar generation from SSP and instead of an antenna, have a passive microwave reflector, we can potentially get the cost of the reflector down to less than $1 billion. Let’s say it’s a flat spinning <8 gram per square meter perforated mylar single-mission heavy payload to GEO straw man. If we spend $1 billion on a ground-based microwave antenna and another $1 billion on a rectenna, we have a 1 GW system that can function as transmission for a 40-year straight-line cost of 1.5 cents/kwh which is about 30% of the cost of SSP per watt with the viable scale of capital needed much smaller. (If you need a VC return, the price must be closer to ten cents per kwh.) The reflector would not be at capacity so additional transmission can be achieved for 2/3 of that. 1 GW beaming for $3 billion would be a pretty satisfying proof of concept. There's plenty of power on the ground to beam to space that's cheap so the proof of concept can be economically viable at this scale. At Hawaii's buy price of more than $0.30/kwh and New Mexico's sell price of less than $0.10/kwh it would pay for itself pretty fast. Space power beaming would therefore be shown to be economically viable without the space generation and thus be valuable as a proof of concept for transmission alone.