Someone asked a similar question as you in this thread:http://www.tomshardware.com/forum/297368-31-budget-build-build
...however, it is roughly a week or two old and the combo prices won't match quite as well anymore. But you can get a decent idea of what you are asking for and what you will have to settle with. Also, try using the format the op used as it helps everyone around here get a better idea of what we can put together.
Bottleneck is typically used term to point out the part or parts in your computer that brings down performance for the whole system. For example, having a system full of great parts but only 1 gb of memory will make your system run seemly run very slow. The bottleneck here is the memory, not enough memory makes your system access the harddrive which is much slower than putting it into memory. To fix, you would have to add more memory.
Cheaper systems can have very apparent bottlenecks if you do not plan correctly. Keep in mind that sometimes people will use the term a little more loosely to point out where your system would benefit the most from. Hope that helps.