I can build obviation grids, null turrets, neutronium armor, ct lab, embassy, harvesters. I can go to a maximum of 5 legion to perform upgrades.

price for obviation upgrade: (per) 5.5 billion credits. (level 5 base)
price for metachron upgrade: (per) 30 million credits. (level 4 base)
price for rift grid upgrade: (per) 3 million credits. (level 3 base)

price for neutronium hull upgrade: 55 million credits. (level 3 base)
price for nexus hull upgrade: (per) 7 million credits. (level 2 base?)

Price for Null turret upgrade: (per) 550 million credits (level 4 base)
price for singularity turret upgrade: (per) 55 million credits (level 3 base)
price for disruptor turret upgrade: (per) 3 million credits (level 2 base)

price for CT lab: 1200 tech parts.
Price for embassy: (per) 30 political favor
price for AI bay/other modules of level: (per) 4 million credits
price for commerce bay: (per) ~500,000 credits.
price for repair bay: 1 million credits + 25 XTS-9 OR 35 XTS-9