You can find many companies are providing uber like taxi rental apps and websites. I will not recommend you to go with that, it will be very cheaper but will not give you a quality product and support.
A customized product which satisfies your unique business model and design will help you to succeed. It will be more expensive to built. The development cost depends on company and location. If it's an Indian company, cost will be $20000 to $30000 and may require 4 - 6 months time to develop, test and launch.
Hope this help you.
It is not difficult to build Uber like app. We are into the business of developing Apps. We get inquiries for similar App from clients having cab / travel business.
I have to say it's not that easy. First of all, it takes many hours to develop such application. Besides, an app like Uber consists of few elements (the customer app, app for a driver, administrative panel). I recommend you to read this article, I think you'll not have any questions after reading - woxapp.com/en/how-to-build-an-app-like-uber/