Hey Swartl, $6875 is pretty crazy high, especially since it doesn't sound like the new boiler is that much better than the old one. If your just looking for someone to do maintenance on the boiler, you can try asking around at some of your local plumbing supply places. They usually know all the local professionals and can usually recommend someone for small jobs. $2200 doesn't sound like a bad price for installing a new furnace.
I have much less experience with forced air, but you should be able to just take off the front panels on your furnace and take a look at the guts. There really isn't much to it when you get down to it. Combustion chamber and a blower. What you'll probably see is that everything is covered in dust and grit. Use a vacuum and clean it out as best you can, then do the same with the chimney cleanout. Take a close look at the burners, yours are probably made of sheet metal and have small slits along the top, sometimes they get corroded out, very easy to replace. Look at the bottom of the unit, sometimes that's rusted out. Give the blower a spin to make sure it spins easily. Usually the biggest problem with these older units is simply that they are so gummed up with dust and dirt that they stop working properly.