burst radiators and pipes - price to repair

[daw]

i am looking at a home to possibly purchase, and it had not been properly winterized last year- the normal plumbing had been drained, but the radiators and boiler were not, and they burst. most of the damage is to the places where 2 pipes join (couplers?) but a few radiators have cracked. the pressure must have been pretty high, as there is black grease like substance as far as 10 feet from the source of the radiator. i'm thinking that the boiler and some of the radiators need replacement as well as the couplers. the house is 3 stories with a basement, 1818 square feet. and really really cheap (around $23usd per sq foot). what sort of price range am i looking at to replace 4 radiators and the boiler? should i keep it as steam or would it be less expensive to convert it to hot water or forced air? any help would be appreciated.

[HayZee518]

those "couplers" are called unions. the black crap is sediment from inside the radiators. to replace the system with either steam or hot water [hydrionic ] system will run about 18,000 dollars. hydrionic systems are "zoned" with their own thermostat and zone valves. steam is usually whole house with one thermostat.