i have the hobart airforce 625. it works great. it uses miller consumables so i'm golden. i bought it brand new for $350. it went for over 3k orginally. i've used it a ton. when i turned it on, i blew the mother board. hobart took good care of me, but i can't say the same for middlesex gas in everett. (it was 5 year old new old stock)
plasma cutters aren't the best for demolition. they are awesome for cutting out brackets and other tasks. i'd make sure it is 220v. if the price is right go for it. lincoln make two types of products, those they sell in the box stores and those they sell in welding shops.
when i get mine dialed in properly, it cuts pretty clean. i quickly learned that when your tips are too worn they affect cutting quality. and as tony said, get an air dryer for it. i used a cheap on from harbor freight and it did the job.