Is this natural gas, or propane?
Either way, a 30 year old furnace can be outright dangerous, and $1,900 for a new one is a good price, if that's the installed price. I had my 15 year old furnace replaced in 2005, but that was because it exploded due to a gas pocket. Blew the chimney right off the roof, and into the woods. Luckily the furnace contained itself, and didn't do any damage to the house.