Building exchange is profitable?
Yes, it is profitable, mostly from charge fees for customers transactions
How much investment it's need?
Consider how much you want to invest into an exchange, domain, web servers, SSL and have to hire some pro about IT or programmers which mean; at least you need more than $7,500.
Where I can promote it?
You can promote it in this forum by using your own signature and make an ANN thread about your exchange, or through every social media such as telegram, facebook, twitter, etc.
How I can avoid or put low transaction cost?
You can't avoid transaction cost, but you still could apply low transaction,
BTC0.005 for withdraw bitcoin and 1% for withdraw fiat currency are convenient and fair in my opinion.
How much time I need per day behind this project?
In the beginning, you need 24 hours a day, 7 days a week, keep an eye to your web and maintain it.
Yes, you need to sacrifice your time and effort to build an exchange.
But, for small exchange, maybe 15 hours per day is enough.
Thanks mate. My budget is around 2K$ so it's not worth to create own exchange for me