My husband & I want to remove a massive 14" high by 15" deep soffit in our kitchen. We have a one story house with an attic. Our HVAC is metal not aluminum and part of it is housed in that soffit with insulation over it. Can we move the HVAC ourselves safely or do we need to hire someone? What can we expect to pay?
It can be very difficult to answer questions such as yours accurately without seeing the situation first-hand. In cases like this that involve electrical, plumbing, or mechanical issues, I always recommend hiring a contractor. That way you know the job should be done correctly and even more important -- safely.
All that being said, it doesn't sound like your job is too complicated. If the attic is directly above the bulkhead being removed, moving the duct up into the space should be fairly easy. There are two issues that would concern me: where the branch line comes out of the main trunk line and whether the line is actually a part of the HVAC system.
It's unusual for a supply duct to be installed in a kitchen bulkhead -- especially when there is plenty of attic space overhead. Are you sure the duct isn't for ventilation from a range hood? Those are commonly installed in kitchen bulkheads and run from the fixture to the exterior of the home. If that's what you have, it may be possible to vent directly out the back of the range hood without the duct going up into the bulkhead or the attic.
If the line is indeed a part of the HVAC system, where it exits the trunk can affect the difficulty of the project. A line exiting from the bottom will require a new piece of trunk line to be installed or the existing hole to be totally closed off. However, if the line exits from the side, you may get by with just removing two elbows and reinstalling the section of straight branch line to the trunk.
If this is the case, you may be able to handle the project yourself. Remember that all ductwork in the attic must be insulated and that the sharp edges of metal duct can cause severe cuts. I speak from personal experience on that issue.
To be on the safe side, you still might want to hire a contractor for the project. I can't imagine the whole job taking more than several hours and they might need a few pieces of duct. I would think that the project could be done for less than several hundred dollars -- that doesn't include removing the bulkhead or any repairs that may cause.