I suspect you will be hard pressed to get anyting over an i3 on a less than $800 budget. Perhaps you hit the standard spots like www.newegg.com , www.tigerdirect.com , www.intrex.com

5 accounts in major city, on a <$800 computer... might be tough. Perhaps if you listed your current specs, people here can help tell you what items to purchase, and how to set up stuff... sort of get the best bang for your bucks.