Unity is one of the easiest game engine frameworks to develop with on the planet. It’s also one of the most powerful.
Free for low profit developers — You can upgrade to pro for around 75$/month but thats probably only worth considering if you have a serious project with some hope of ROI — you can potentially get yourself into the industry with very small investment or even use it for other non game projects that require audio/visual/interactivity.
Many of the posts on this site are unity related. Unity makes great use of c# as its scripting language of choice. Throughout this site you will find snippets of code which may be useful.