How much will you spend for early marketing such a (concept) demo video composing？

For a marketing concept video without a product, I think the time requirement will be crazy and the price is going to be high as hell. If you have the product ready, you will still need some budget and scenario for a promotional video, but it's gonna be easier then that an abstract conceptual video. But if you want just to showcase the features of your product without heavy editing and any rendering, just to do the demo easily and quickly, feel free to try our app that we've been working on with @imanmoaz https://www.castofly.com/ You can do everything required for your product demo there and videos for potential investors (MVP, proof of concept) if you don't have your product yet. You can record your screen, or webcam, or both at the same time, or import a pre-built video. And yeah, it's free. If you have your product public, please send me the link to it - I'll check it out and record my positive review :)