It is a top/bottom style duplex with a flat roof and a basement so there should be no issues around ducting. each floor is around 1,100 sq ft  Any idea how much I should be looking to get this quoted for?  

I thought this issue was resolved it is not resolved now I had to have a wall rebuilt that was ate up with mold luckily I have caught the water early this time and cut the drywall back so the only mold food is the bottom wood beam. 

The contractor cut some corners with the bottom unit that cost more to correct in the long run.

Bottom of unit would remain commercial. 

I find myself when making offers, obviously wanting the bottom bottom line price, for good reason.BUT, when does the potential of losing the deal over a few thousand dollars become not worth it?  

I have never used them nor installed them, but my first thought was the same as @Brian Burke, you may save money on the install but in the long run with maintenance and possibility of hazards - that alone would steer me away from them, i like to sleep at night - i think you are better off venting once and forgetting, it will be done. btw, they are $15 at HD. and this is what theirs look like and how it works, the bottom of the container is filled with water, the lint is held by the water when it is forced in and then has to be cleaned and refilled after each use.

keep in mind fake lenders are the new Nigerian prince scam of real estatethere is no private money that is less than about 10% apr.. bottom line.

I find myself when making offers, obviously wanting the bottom bottom line price, for good reason.BUT, when does the potential of losing the deal over a few thousand dollars become not worth it?

Which marriage pattern is more common among the bottom 99.9% millionaires in America?

Bottom line is if you can afford the upgrade i think you should go for it.