In reply to mike123:
Your best bet is probably a used Mac Mini. I'm a big fan of the mini and it has a loyal (but small) following of developers, home entertainment enthusiasts and everyday mac users who don't fancy the whopping price tags on the rest of the range.
The latest 2014 model is quite cheap new, but was given a hostile welcome for being less powerful in many respects and less upgradeable than the 2012 model. The entry level in particular is very weedy, although perfectly adequate for some needs. Hence the top-end 2012 i7 quad-core is in high demand on ebay. For your requirement, your best bet might be trying to pick up an entry or mid level 2012 model - they go for around 300 to 400. If you can get one with fusion drive or SSD (or upgrade afterwards - fiddly but possible) then that will give you much better performance as the stock mini HDDs are not the best.