Normally, if you're going to use a dedicated GPU, you want to pick the 860K, because you won't be using the integrated GPU portion of the APU. However, right now the 7600 is $20 cheaper than the 860K (http://pcpartpicker.com/products/cpu/#sort=a7&page=1&k=26&qq=1), so it would fit better into your budget, especially if your budget is that limited. Note that, while a Skylake Pentium is also running about as cheap, its version of the Intel Iris graphics is nowhere near as good as the other Skylake chips, & doesn't run as well as AMD's (http://gpu.userbenchmark.com/Compare/Intel-HD-510-Desktop-Skylake-vs-AMD-Radeon-R7-Graphics/m38088vsm8791). It's sole recommendation is the ability to eventually replace the Pentium with a much, much better Core i5.
You can CrossFire the A8-7600 with a Radeon R7 card, but you're going to be limited to the R7 240 or R7 250 (http://www.cpu-world.com/info/AMD/Recommended_graphics_cards_for_AMD_dual-graphics.html). Neither of those is going to be super-great, however, plus you're risking lack of CrossFire support in your games.
Basically, with your very limited budget, you want to build a low-end system that depends on the integrated GPU built into the CPU, & then plan later on to add a better dedicated GPU. The real question, however, is what system you currently have. A $140-150 budget might allow for a better upgrade to your existing system, rather than replacing the core parts.