APPLE A1347 MC815LL/A 2011 Mac Mini 5.1 Core i5 2.30Ghz 4GB 500GB - HDMI
These older Mac Mini’s are a great bargain at about $300 for a 2011 Model that you can actually upgrade vs the current 2014 Mac Mini models that are not upgradeable at all.
But, if you were to make a few upgrades to this model you’d have a great Mac on the cheap.
The first upgrade is the RAM. This one already has 4GB and this might be fine but you can double the ram to 8GB for about $50.00 on sale and then sell the 4GB of ram to offset the costs of the upgrade.
500gb is a fine storage amount for most, but if you can afford it replace the slow standard hard with a much faster SSD drive. Prices are dropping and now you could even get a 500GB SSD for under $200.
To summarize if you shop around a bit you could have a fast Mac Mini with fast storage and enough ram for most tasks for a total of about $500.00