As many have mentioned, there are a lot of cheaper alternatives. However, Copics do a lot of things very well, whereas most of the cheaper options do one or two things well but fall behind in other areas.
Like most people have said, the Prismacolor markers are a pretty solid choice if you want Copics but don't have the budget. I think the biggest shortfall for them are the nibs; they just don't have the same feel and nowhere near the same variety. The one thing the Copic Classics have going for them is the sheer amount of different nibs you can plug into those things.
If you're looking to use these markers for blending, another option are the Chameleon ColorTone pens. They are cheaper than Copics and specifically designed for blending.
We recently put together a huge interactive comparison guide on all the different types of Copics on our website. Down at the bottom you will find a section devoted to Copic alternatives:
http://colorgaia.com/copic-markers-depth-review-comparison/