This is what I'm building soon for Gigabit WAN. (We currently only have 107/5, but ISP is building a gigabit fiber network as we speak, should be out be end of the year)
Thermaltake Urban S1 Case
http://www.newegg.com/Product/Product.aspx?Item=N82E16811133257
Corsair 450M 450W 80 Plus Gold PSU
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139058
Core i3 4130T Haswell 2.9GHz 35W TDP
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116947
MSI H81 mATX Mobo
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130752
4GB Mushkin Blackline PC1600 DDR3 (already have so not included in price
500GB Seagate HDD
http://www.newegg.com/Product/Product.aspx?Item=N82E16822148767
2x Intel PCI Express Gigabit NICS
http://www.newegg.com/Product/Product.aspx?Item=N82E16833106033
Total cost is $418 after shipping
Should be more than enough for your needs as well. which is why I posted it.