It seems that SP housing would be a big strain on SE servers... so if that's a consideration in setting the price you could argue that SP housing should be more than FC houses. Honestly, I've never been in a good FC, and haven't enjoyed FC housing at all... so I can see demand for SP housing being very high.

I wouldn't mind if they did an auction system which would let the players set the price... and I think it would be HIGH... and maybe a way for SE to find and ban gil buyers ;p