The iMac is Apple's main desktop computer today, and it's certainly come a long way since the original Macintosh, but if you're looking to save some money and still want a relatively-modern iMac experience, the 2007 iMac is a good option.
It was the first iMac to incorporate the modern aluminum design, and was the first model to come with a 1TB hard drive.
It's also still new enough that you can run OS X El Capitan on it, and if you're feeling particularly handy, you can even upgrade the memory and swap out the hard drive for an SSD for better performance.
You can usually find these older iMacs for around $200-$300, depending on the components, but I was able to snag a 2008 iMac for $150 at a garage sale last summer, so keep your fingers crossed.
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