Comixology is a great app. New comics come out every Wednesday. Sometimes there are .99 cents sales, but regular prices are between $2.99 to 4.99 per digital comic. I have noticed that some series are reduced after a month, you can wait a month and get it for $1.00 or $2.00 less.
One thing to note, and as far as I know, because everything is digital, I am not sure if I actually own the comic I bought or I am licensing to read the comic. If Comixology is to shut down tomorrow, will there be a way to have a copy of all of my hundreds of digital comic books? I can do that with ebooks via Calibre but digital comics is another matter.