Dell currently has a decent deal on an i7-6700 system that would make a good high-end Blue Iris box.
http://slickdeals.net/f/8866231-dell-inspiron-3650-core-i7-6700-win7-pro-desktop-amd-r9-360-2gb-gddr5-16gb-ram-2tb-hdd-wifi-bt-579-with-f-s-at-dell
Note this is not one of the much-loved optiplex desktops with 3 year on-site warranty. This one comes with a 1-year mail-in warranty which you could upgrade for about $80. Warranties are always a gamble.
Also, it comes with a modest AMD graphics card. For a dedicated Blue Iris machine, you'd probably be better off taking it out and using onboard graphics to save power. You'd also want to upgrade it to Windows 10 so you could use hardware acceleration while running BI as a service.
http://slickdeals.net/f/8866231-dell-inspiron-3650-core-i7-6700-win7-pro-desktop-amd-r9-360-2gb-gddr5-16gb-ram-2tb-hdd-wifi-bt-579-with-f-s-at-dell
Note this is not one of the much-loved optiplex desktops with 3 year on-site warranty. This one comes with a 1-year mail-in warranty which you could upgrade for about $80. Warranties are always a gamble.
Also, it comes with a modest AMD graphics card. For a dedicated Blue Iris machine, you'd probably be better off taking it out and using onboard graphics to save power. You'd also want to upgrade it to Windows 10 so you could use hardware acceleration while running BI as a service.