With the cost of oil and gas, the payback time for a new boiler, even an expensive one will be fairly short.. You can get by with supplemental heat from a coal stove or hot air furnace and try to circulate the hot air,, but this is often frustrating.. No matter what any coal fired supplemental heat will help keep the fuel bills down.
Read, read, and read some more,, there are dozens of topics and threads on similar subjects here..
I'd PM to scraper_23jr or to coal berner about a used EFM or other steam capable boiler. Matthaus may have a steam capable boiler as well.. I would plan on buying a good steam boiler eventually,, new or used, but I'd stay with the steam system for comfort and even heat distribution.
Do you have an extra chimney in the basement or next floor up so you could add a suplemental hot air stove??
Hope this helps. Greg L'