If you're looking at a more mainstream system, such as a Castle Creations Sidewinder (their lower-end but still crazy powerful ESC/motor combo), they got for around $130. Higher up is the Castle Creations Mamba Max, which is around $160-180 I believe. There are other brands that are also good, but I am most familiar with Castle. If you're looking to save some money and still get a great system, the eZRun systems are great bang for the buck. They are made in Hong Kong, but probably one of the highest quality pieces of equipment you can get from there. An eZRun system goes for anywhere from $45 to $100, obviously very dependent on the output power and features. Another thing to consider is sensored vs. sensorless, but that's a whole 'nother conversation. All the systems mentioned above are sensorless and they all work great.

The bottom line is that you'll spend around $100+ for a good brushless system, and since you already have a LiPo you should be in business quick