Essential has all the basic features for skeletal animation. It can do a lot and there is a significant jump from not using Spine at all to using Spine Essential. These animations were all done with Essential:
http://esotericsoftware.com/files/Gamasutra-Carlos-Cavalcante-Tips-to-create-funny-and-juicy-character-animations-with-Spine-basics
Spine Professional adds a lot more features: meshes, constraints, etc. All of that stuff can be very powerful, but can also be a bit overwhelming. I feel some users find themselves focusing too much on the fancy features instead of the animation itself. I think it's a good plan to start with Essential and only move to the more advanced features in Professional after mastering the basics.
Don't feel pressured by the sale price. While we sometimes need to raise the price, it's permanently marked like that to reduce the requests for us to do sales. We list the product at the price we feel is fair. We don't do sales because it's unfair to customers who missed the sale.
