About $150 per year for "consumables" -- chains, tires, tubes, bar wrap, chain-lube, patch kits. Maybe another $125 per year (on average) for new shorts, jerseys, gloves and helmets. Add another $125 per year (on average) for replacing worn out or broken components -- brake pads, cables, etc.

So, I'd estimate about $400 per year to keep two road bikes in operable condition.