Any electrical/electronical engineer here?

Ask your senior engineer.
Or just Google assembly houses (in your own country or in China) and ask how much their full service, including components, PCBs and all, costs.

>Any tips or advices.
4chan isn't really a place for this.

Look up component industries and pickup the phone or send emails.

>Any tips?

Sounds like you require advice from a business perspective and not an engineering perspective.

>>1140664
In my previous company where they design their own PCB, the "main" hardware engineer was making BOM but I don't get where the prices/unit could come from.

Is the PCB manufacturer the only one to provide component @ his price or could I find a best price in my country and make them send to factory?

I'm kinda good for prototyping but I'm very bad at managed a large number of PCB board.

>>1140671
Yes, you can shop around to find the cheapest PCB maker. Same with the stencil maker. You can also buy all the components by yourself and send them to the factory.
Or you can just send the required documents to the assembly house and ask them to do everything. Certainly it costs more, but you seem to need all the possible help.

>>1140713
>>1140713
The production start is planned on december 2017 at the better. But I am already thinking about the cost and I am asking not to seems dumb with manufacturer.

Thank for the info

If you went to one manufacturer, then you would be stupid, unless you have been through this process before.

You call, state your requirements and timeline, they place a bid.

Post your gerber files and BOM. Also small run like 20k units is the size of volume for a small contract manufacture. Price will vary by the production companies abilities (manufacturing tolerances, pre-testing, automation.