Below is a 54" Independent hood.

16 gauge 304 SS with seamless contruction.

Very very high end.

Independent has gone bankrupt because they lost their contact with Wolf-Sub-Zero,the bad economy etc etc etc.

So there is no factory warranty but a hell of a deal.

$999.99 plus $85 shipping.

Here is a link that might be useful: LINK

You can also look at Best by Broan. I have the K260 model at 54" over a 48" range. It's only 24" deep, but I have it mounted 3" off the wall. I believe it was about a $1000. You can also consider an insert from them too.

We have the same Best by Broan hood as jscout that we bought for a similar price.

Tradewind is VERY inexpensive for a 54" with baffles and dimmer lights and it is quiet and very easy to clean. Here is the link. I have used mine for 6 yrs and posted lots of pics. Ours is over the 36 " Caldera gas cooktop and our Miele built in deep fat fryer..the hood gets a work out !!

Here is a link that might be useful: Tradewind

Your tentative plan to have a carpenter build a wood hood around a liner will probably be the very best way to get a great hood for very little. Ours was built by the framers who built our home from stock boards and moldings to my design. Literally a couple hundred dollars plus materials. If you don't like the estimate you get from the cabinet guys, you might try getting more from independent carpenters not associated with the kitchen industry.

we did what rosie suggested...looks wonderful and very inexpensive. c

Or, use the hood you have over your range and place your hob in another location with a smaller hood. Double cooking stations are becoming more common in kitchens these days just like double dishwashers and prep sinks.

Here are some ideas for your carpenter. Too bad you could
not diy than you could really save money.
~boxer
who wishes her ideas were super easy to put together.

Maybe cover a frame with copper

trim with a copper strip

Here is a link that might be useful: past post

i got an independent 52" liner at an outlet for $600 a while ago before they went bankrupt. i think you might be able to find some even better deals on it now since independent went bankrupt. As long as your abakka blower uses a 10 inch duct, you can use the independent liner.
i plan on having a custom hood made out of precast concrete or stucco because those metal ones are sooo pricey (but beautiful). after you add the thickness of the hood, if you make it at least 1 inch thick on either side, you would have a deep 54" hood. it is possible your contractor can frame one for you too.