For the big businesses they are running things like enterprise editions of ORACLE or MSSQL server along with all the middleware and application servers on top, which makes the barrier to entry for the small guy pretty high, since these take some serious time to master which is why you normally only ever see the top highly paid and experienced system engineers handling tasks like this in the big corporations.
Some may bring in a small business to try and accomplish this tasks but if it is a large business it only takes a small team to really accomplish this and fully automate it (two to four top system engineers, a software engineer to create interface for management and the system engineers, along with insuring the API and other security checks for compliance and SLAs are in place.
If you want to get in on something like this insure you have the proper credentials for what the company uses in their infrastructure (SAS, SAP, ORACLE, Microsoft SQL Server, Hadoop, Spark, .NET, Java, C/C++, along with vMWare products, Excel Macros, Office plugins, etc.) and have experience doing data migration, optimized SQL queries and ETL operations. As some of these companies have petabytes of data to deal with, so your small time 200GB database would not give you the experience necessary to work with these massive systems or the insight into how to write proper queries to work with these systems unless you have being doing it for a few years.
If you have experience in many of these you might be able to do it. To keep things small I would recommend building out some prototypes that end up as high quality services or products and go in as your own business. This way you get to keep the work you create, make more off your work and get to benefit off of word of mouth and can get even more customers if they really like your work.
It is hard work to get things like this automated in the various environments but it can be done. Those that come in and do it right benefit heavily as they can focus on more important things like research and development.