BlueBill:
I2C port expander to a pair of ULN2803As to your relays should be enough. The relays don't require regulated power and their current needs are in their datasheet. Get a supply that has at least 50% more current then you need.What are you switching and which relays are you planning on using?
What he said. Use a PCF8574N 8-bit IO expander. Its the easiest to work with.