Just understand then that you're paying for the experience, and get the cheapest cards you can get to crossfire. Once you get it up and working, then put in your actual GPU you use for gaming.
the reason that I'm saying this is that crossfire(and SLI) never produced exactly what was promised. The drivers are buggy when using multiple GPU's and also not all games support multi-gpu's. That's why I say to get the best single card you can afford. If you decide 3 years for now you need an upgrade, then SLI or Crossfire may be a viable option because you could probably find a used GPU to match yours and get a reasonable upgrade for very little money compared to newer GPU.
Honestly, you're going to be hard pressed to build an SLI/crossfire setup at that price range. I personally would go for a 970 or maybe a 980 which will run around 300 - 400 dollars depending on which you buy and then build the rest of the rig around it. One 970 or 980 is going to be far superior to an equivalent price range SLI setup.
Just understand then that you're paying for the experience, and get the cheapest cards you can get to crossfire. Once you get it up and working, then put in your actual GPU you use for gaming.
the reason that I'm saying this is that crossfire(and SLI) never produced exactly what was promised. The drivers are buggy when using multiple GPU's and also not all games support multi-gpu's. That's why I say to get the best single card you can afford. If you decide 3 years for now you need an upgrade, then SLI or Crossfire may be a viable option because you could probably find a used GPU to match yours and get a reasonable upgrade for very little money compared to newer GPU.