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Look up ubiquity products. Pretty much purpose built to do what you seek. They have a bunch of hardware and it can be a little tough to wade through but it is cheap and works extremely well. I have done exactly what you are looking to do with about $400 worth of gear.
http://ubnt.com
There are dedicated dealers out there but I just research what I need and buy from amazon
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After using every type of wireless router and/or access point you can name, short of the extreme high end (thousands of dollars per device), I settled on Ubiquity. Their produccts are perfect for outbuildings and extending networks, are easy to manage, and I have not rebooted my equipment in over a year. Their support isn't fantastic, but they have user forums that are a wealth of information. Don't use their latest software/firmware (latest-and-greatest always seems to be released with a metric ton of bugs) and you will be GTG.
I have on Unifi AP covering a 3000sq ft two-story home (four bars for all devices anywhere in the house), and an Air Wire system connecting a small switch upstairs to the main network downstairs (both locations are were I want to run wired devices, not wireless devices). I am looking at a couple of their newer products to upgrade the Air Wire system. They have a huge range of products that can cover pretty much anything you can throw at it as far as general home/ranch/farm use goes.
They have inexpensive products (relatively speaking) for which a 600ft shot (unobstructed line of sight) would be super easy (150mbit on the low end), and have other products with more signal amplification that would get you there if you were shooting through trees.