I agree with EricMA - you're a great candidate for a refurb computer.
Alternatively, you could get a brand new Intel NUC - for something like $150 - or a competing and similar product. They're even less powerful machines, but they do the job just fine. Downside is they tend to come without a windows license (and might come without a hard drive, depending on the product...)
To keep a $200 computer working fast, just make sure you don't download stupid shit (toolbars, screen savers... emoticons) and you don't watch porn on weird fringe sites. And you run a registry/cache/etc cleaner (eg ccleaner), malware remover (eg malwarebytes), and antivirus regularly.