[schiffern]

>3) hope that somehow it will become much cheaper through windfall technology developments in other fields (not impossible, but certainly not one that I would bet on)

Brain uploading. I don't know if Kurzweil's "$1000 computer by 2035" prediction is right, but we'll certainly have it by the end of the century.

Accelerando features a good exploration of this. Your interstellar spaceship is a laser-propelled computer the size of a soda can, with everyone's brains simply uploaded into it.