I do know that to make a good, fully functioning, average sized, Secure type base (Capable of placing two power generators compared to Hidden type's single), with a fair splatter of defences and decoration costed us about 25 million prestige. That included decorations, several vault rooms, two small securitcy checkpoints (a choke point and security corridor), two small work areas, medical facilities, raid teleporter, control room etc. Which is a heck of a lot of prestiege.
I don't know how things will scale out in the long run, I don't know how long it will take untill Gangs can start setting up bases of similar size, we'll see later down the line when people start building up levels.
