Lee if you are going by yourself,you should be able to get a ticket to just about anything as they almost always have single seats available. Try Ticketmaster.com or Broadway.com and you should find a decent seat for $100 US. Can't help with the location of TKTS at the Seaport but the Seaport itself is in lower Manhattan at the end of Fulton Street at the East River. A confusing neighborhood to find your own way around. I would suggest if you are going to go, just get in a taxi.
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Helen
Oh sorry misread the post that you didn't know how to get to the seaport