Barton 2500+ can be bought for less than $100 but can be overclocked to a 3200+ putting out little heat with the right cooling.
http://www.newegg.com/app/ViewProductDesc.asp?description=19-103-379&depa=1
For motherboards, my advice is you should stick to the nVidia nForce 2 chipset.
http://www.newegg.com/app/ViewProductDesc.asp?description=19-103-379&depa=1
For motherboards, my advice is you should stick to the nVidia nForce 2 chipset.