There are few services out there which offers creating a brand new exchange platform for you, you can search for them in google.
Just tell them what features you want in your exchange, they will give you quote.
Building exchange is profitable?
How much investment it's need?
Where I can promote it?
How I can avoid or put low transaction cost?
How much time I need per day behind this project?
Depends upon how you will run it.
ask the one who will build it and add around $2000 on that which you might have to spend on initial advertising.
----------------?
Depend upon how successful your project will be in future. You might have to spend more than 8 hours a day in early days because you might have to handle lots of advertising campaigns.
My budget is around it.