Gas and Oil Home Heating Furnaces - no heat or air

i wrote in several weeks ago about a problem with my central air/heat unit. i have some more info. i have a rheem unit model # RHQA 1210 BCS. over the last six months it has started not producing heat or cool air. the unit is clean and there is no obstruction around the outside unit. the blower comes on and air comes out of the vents but it is the same temp air no matter what setting it is on. could this be a lack of coolant? any other causes? the change in efficiency was gradual. also how much is a reasonable price to pay to have it serviced.
thank you very much for the help. this is a great website!

brian, feeling temperate

Feeling temperate, that's good. Have a pro look at it. Since you say the heat and cool operation has gone downhill gradually...It could be a veriety of problems. From stopped up filter,coils, collapsed return duct(sounds like you have a package heat pump), freon, bad compressor, reversing valve, etc.