Screenshots represent as they exist currently in Beta
Keep Costs: Click image for larger version Name: Keep Costs.png Views: 4678 Size: 155.6 KB ID: 790
Housing Costs: Click image for larger version Name: Housing Costs.png Views: 4574 Size: 167.2 KB ID: 792
Stronghold Costs: Click image for larger version Name: Stronghold Costs.png Views: 4587 Size: 78.7 KB ID: 791
Stronghold Materials Needed: Click image for larger version Name: Stronghold Materials Needed.png Views: 4587 Size: 87.2 KB ID: 793

These are available in each NPC city, with Keep and Housing vendors.

The upkeep cost for a Tier 1 Stronghold is almost 1 gold every day, and the charge starts when the initial blueprint is placed. So have your coin ready to go.