The answer is not simple, all the parts which make the complete system need to work together and be compatible with the software. You should be able to build something for under $2k, make sure you pick a processor with lots of cache, AMDs are cheaper for more performance. A good quality motherboard, as much quality ram as you can afford(suggest 2 GIG minimum) balanced with as much as you can afford on a quality video card. These days even low end video cards run rings around their predecessors and have big on-board memmory and fast processors. All the other bits (hard drives, dvd reader/writer etc) are very cheap even on expensive systems.
Hope this helps
