Hi guys, what is the cost of making gambling casino based on btc?

It will vary on what site you are tending to make because i do believe that a dice site do have different cost than building with a sports betting one.
Talking about the cost? Dont have much idea but for sure lots of factors will affect the total cost yet it will depend from UI/UX design until to marketing stuff etc.
There are some threads that might be useful for you to read up and might able to get some ideas.

https://bitcointalk.org/index.php?topic=1637945.0
https://bitcointalk.org/index.php?topic=5131758.0
https://bitcointalk.org/index.php?topic=1760302.0

Most part of cost it's license in different countries. For example, in UK:

Quote

The full gaming license is a single license for your gaming business – the application fee is £5,000, the annual fee is £35,000.

Here is more - https://www.gamblingcommission.gov.uk/for-gambling-businesses/Do-I-need-a-licence/Types-of-operating-licence.aspx

annual fees you need to pay year by year and noone fuck about do you have profit or not. Some countries (like mine for example) don't have even the opportunity to buy license and your service can be blocked anytime.

you can try of course without permissions, but you should be ready to get into blacklist (your site and all it's infrastructure will be lost).

Compromise - to buy license in offshores (price list - https://meliorgames.com/gambling/online-gambling-license-how-to-get-it/)