Any used Computer with a multi-core (no Pentium4!) is fast enough for your purposes, since you don't use them often judged by your post. (I strongly advise for at least an Intel i3 though)
Photo editing: Here's why you should use a dual-core and at least 4GB of Ram. Also at least 500GB of disk space. And a second /external HDD for backup.
The Rakuten has a small HDD and only DDR2 RAM. Pretty old. But cheap.
From the long Lenovo list linked by DocLago this looks like your new PC:
http://outlet.lenovo.com/SEUILibrary/controller/e/outlet_us/LenovoPortal/en_US/catalog.workflow:item.detail?hide_menu_area=true&GroupID=445&Code=57RF0151#
Processor
Intel Core i3-3240 3.4GHz 3MB Cache
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Operating system
Windows 8 Standard 64 - English
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Graphics
Intel HD Graphics 2500
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Memory
6GB (2GB & 4GB) PC3-10600 DDR3 1333MHz SDRAM UDIMM Memory
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Hard Drive
1TB, 7200RPM Serial ATA 3.5" Hard Drive
RAM and HDD bigger for your pictures, fast 2-core. The Intel Graphics makes Full-HD Videos run. It does everything fast except Games.
$312.16 (without coupon) is slightly over your budget, but it is really worth a few extra bucks.
Try to use LibreOffice (more free and (I think) better version of OpenOffice). If you are adventuroues, get a dual-boot Linux to have a look how to get by without paying Microsoft. Its saver and faster, too.
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I just want to make a point for a different choice for users who sit before the screen for several hours a day.
I'm a sort of Computer Fan and the energy price in germany is very high (next year I will pay nearly 27 €-cent per kWh), so I prefer to buy them new.
This way you get a better Watt-Efficiency, which gets important of you use the computer for several hours each day at these prices. Also newer systems tend to be more durable, of course.
For Office use you can have a look at small form factors. I just have seen a 280€ (hardware only) small box with an Intel Core i3-4100U (Haswell is the newest generation). About as big as a netbook, only higher. No DVD-drive! (you can get external)
That little thing had about the power of the linked rakuten. But with only a 40W power supply (and likely dont use more then 30W) and very silent ;)
In short: If you use the computer very much and could use more space, better get a small new one, even if it costs 400$ and has no DVD-drive.
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build a new one:
YOU dont need to. But if you need to, get a half-geek like me who has done it several times from somewhere around you, set him a tight budget, say what you want to do and say that is should be a silent computer (I always stress silent).
Let him search for a day for the best parts.
Then let him come to you on a weekend and let him show you how to do it. This way you also learn how to make "repairs" like changing a RAM or a drive.