How much it cost and time frame needed for developing platforms like coinbase e.t.c.
More than you have, if you are asking that question on an Internet forum.
Then we have these super-cheap "exchanges" and platforms you can find on the internet where you'd probably get a copycat of some exchange with lots of flaws and you just won't know where to start from without a good team behind your project. IIRC, I've seen some $50-200 exchanges for sale even here on BTCTalk. If you want something serious, that's a very bad idea. Security is the top priority for any crypto exchange imo.
It is why my above answer is not just snark: This is how users wind up losing money. Nowadays with rampant KYC nonsense, it is also how their dox wind up being traded on underground criminal markets.
Somebody posting
on an Internet forum to price out this type of project, with no idea of what work is involved, should
ipso facto not even be thinking about starting an exchange—not even
dreaming about it.
A good Development and Technology discussion from two years ago:
Bad Code Has Lost $500M of Cryptocurrency in Under a Year.
I cannot resist:
Put it at 150K$ and 18 months time frame before releasing version 1.1
OR
200K$ and 12 months for an aggressive project with more high skill devs.
If I budget for an aggressive pregnancy with nine highly skilled mothers, can I make a baby in one month?
At least, that is the business schedule for the prematurely released baby-1.1.0, which will be deprecated with the release of rebranded Baby 2.0. We keep its DNA in git, so that the dev team of mothers can pull patches into their own decentralized clone repositories.