There is no physical reason why it can't be cheaper. For starters, solar power is 4x better in space, so you need 1/4th the area of panels. But also, data center costs are skewed by things like permits, environmental reviews, and (increasingly) lawsuits.

Terrestrial data center costs are only going up, while space tech costs keep going down. It is plausible (but not guaranteed) that they will intersect at some point.