Cheap Carbon Filters

I know there's a multitude of DIY carbon filters for around $20 however I was wondering how reliable these carbon filters on ebay are.

http://www.ebay.com/itm/VenTech-4-x...112426?hash=item3d10a2d72a:g:mVAAAOSwFMZWsCnD (This is my first option)
$52.40

http://www.ebay.com/itm/Hydroponics...hash=item4ac2b52841:m:mwLkmxbapmjfYxLYees37oQ
$39.87

http://www.ebay.com/itm/4-6-8-10-Hy...hash=item35bf24de80:m:m_TFJ864yxHhwCPd_ZTy5Fw
$42.00

http://www.ebay.com/itm/4-Inch-Carb...hash=item1c41bac4b4:m:m9sQZUzr7jrAZf2orDigQJg
$36.95

The grow space is 2'x2'x4'. 16 cubic feet with an 80 cfm fan.

I've heard coconut fiber will fail before the grow finishes.

I know skimping on this part of the grow room is not advised but budget is an issue.

You can get a nice fan and filter combo on amazon for 150 160 bucks