Need help fast my vents have cool air coming from them the furnace blower is working the furnace pilot light comes on and goes my thermastat says 78 inside but is set for 86 what could the problem be and how much might this cost

Are you saying that your pilot does not stay lit that it lights and then goes out, it could be that the thermocople is bad if that is the symptom your having, those are fairly simple to replace if that is what the problem is. If the control module is bad then those can be a little costly depening on mfg.

What kind of pilot do you have and if the pilot lights does it light the burners.
Why do you have your furnace set at 86?
There are several problems that can cause what you described. Give us some more info so we can pinpoint your problem

What kind of pilot do you have and if the pilot lights does it light the burners.
Why do you have your furnace set at 86?
There are several problems that can cause what you described. Give us some more info so we can pinpoint your problem
There are 5 burners on the furnace I turned up the thermastat to see if it would kick on the blower is burning and its cool air and the and the furnace pilot comes on and goes off and does it again

Is the pilot a flame that you can see or does it make a bright light which is called a hot surface ignitor, this is suppose to light the burners and then in a few minutes the blower is supposed to come on and blow warm air out into the house.

If your furnace does not have a pilot (small flame) but a hot surface ignightor or a high voltage spark across two electrodes check and make sure your gas valve is turned to on posistion as well as gas line ball valve on gas line itself. Does your furnace have a control board with a flashing light flashing a code, the code sequence or legend is useally found on the door. Also make sure no wires are unpluged from the pressure switch. The pressure switch is the round device that has a rubber hose on it going to a collector box on the furnace,and two small wires going to the gas valve. Really want to help, but need more detail