You can hire a web development company in India on a per-project basis, where the cost of the project completely depends on the scope of the project. When you hire on a per-project basis various teams (UX and web designers, front-end developers, back-end developers, testers, etc) would be involved in your project at different stages and there will also be a dedicated project manager assigned.
Another option is to hire a dedicated web developer in India on a monthly basis. In this model, the web developer (or web designer or front-end developer) would be working exclusively on your project and all works/tasks will be assigned directly by you. The pricing here would be hourly and usually calculated on a monthly basis.
At Ainwik infotech, we do offer both of these models.