Microsoft does have Express Edition for free but there are many limitations to the product. Additionally, the Express Edition does not have all the features which any enterprise would love to have. Unfortunately Microsoft does not have a full version of SQL Server for developers. However, one can for sure purchase SQL Server Developer Edition for USD 59.95 from Microsoft store. It includes all the functionality of the Enterprise edition, but is licensed for use as a development and test system, not as a production server. SQL Server Developer is an ideal choice for people who build and test applications.
Remember you can’t use this version in your production server but it is a great product to test out various new SQL Server Features.
Reference : Pinal Dave (https://blog.sqlauthority.com)