Removing an oil tank like Bonka said can be fairly cheap. Prices normally start at around $2000-$2500 depending on machine access.
usually the problem lies if the oil tank has been leaking for years. When the oil starts leaking, the oil leaks into the soil in a cone shape and really messes up a large area. Remediation and hauling gets pretty pricey from there as its dig as deep as needed till you don't smell fumes.
I was a contractor earlier this year for a new development on W.41st in Vancouver where it had a serious leak from the oil tanks in 2 out of the 4 properties. The leak was so bad that it went under the house and stalled the demolition of the properties till the engineers decided what to do next.
