Heat sinks cost 500 C-Bills each, and DHS simply count as 2 HS.
Regarding repair costs, the only information I have is about armour. For Mech armour it's repairCost = "0.5" repairTimeMultiplier = "4.5".
No idea about broken heat sinks, disabled weapons, coolant refills, or even if they cost anything to fix. Easy enough to check for coolant, though.