Build me a webapp

I need to develop a complex quoting web app which allows small to medium sized businesses to produce quotes quickly and efficiently. The look, feel and basic functionality and integrations will be similar to the following website: https://www.quotientapp.com and most quotation apps on the market. However, there will be more integrations and also automations. For now I'm just looking for a quote to get a similar app to that I mentioned. The app should be developed on an open API basis so that all / most functions are accessible through API calls. The app will be cloud based and should be rapidly scalable and well documented.

In your response I need you to provide:
- Cost (Say whether estimated or fixed)
- Breakdown of the cost
- Tech stack that you recommend and will be using
- Project duration / timelines
- Support requirements - details of ongoing support of the application and costing
- Details and links to any similar projects that you have worked on
- Links to your portfolio of apps / websites that you have developed
- Your CV of qualifications / skills

Thanks!