What does it cost to get a hot air balloon to 30,000ft?
A Hot Air Balloon should be able to reach 30,000 ft just fine as according to Wikipedia the world record altitude for Hot Air Balloons is 69,852 ft.  Besides the necessary survival gear for the occupants (Pressurized oxygen and environment suits) a special propane tank would be needed as according to wikipedia:


  However, if the liquid propane in the fuel tanks is too cold (0 °C/32 °F or less) it does not generate sufficient vapor pressure to adequately feed the burner(s). This can be overcome by charging the fuel tanks with inert gas such as nitrogen or by warming them, with electric heat tapes for example, and insulating them against the cold.


Another thing to consider is that you would need special permission from the FAA to go into Class A airspace which goes from 18,000 to 60,000 feet MSL. Usually only IFR rated aircraft can fly in this airspace.  The FAA may require you to fly with a radio and/or transponder if you do get the permission to fly in this airspace.  

I do not know how much propane would be required as I don't fly Hot Air Ballons but it would probably depend on the outside air temperature (less fuel in colder air).