If you know which cpu, graphics card etc. you would like in your new PC try Cougar. With their website you can configure your PC and see how the total price changes by which components you choose. This way you can put together a PC with all the components you would like and see if it comes within your budget.
I bought my present PC from Cougar a couple of years ago and can thoroughly recommend them for build quality and customer service. They are very happy to discuss configuring a PC over the 'phone and are very knowledgeable.