Blender isn't anything like After Effects, and would be used in conjunction with not as a replacement for it. To be honest, I think you're going to struggle finding a cheap alternative to such a high-end application.
why dont you just do the 30 day trial of after effects when you need it and if you really like it then see about getting a second hand copy off eBay or something? make sure you get original discs though else it can be havok!