Make your own. I don't mean this in a sarcastic or rude way, but try to make your own. Of course it will require work, but it's not only a great learning experience but it's also very fun (in my opinion of course). I'm assuming this is going to be 2D so that makes it a ton easier than working in 3D. Also, if you make your own then you have full control over every aspect and can really make it your own. With that said, there won't be any free good RPG engines available for 2 reasons:
1. They are a decent amount of work.
2. RPG's are very game specific and to make a universal engine would be very difficult to do while keeping it cheap/free.
My final words, try to make your own. Keep it simple to begin with, but when you grow more comfortable then advance the engine further and further until it's complete.