I think the K&N and mobile one are the same filter. look closely at both of them. same part numbering scheme, same look, same numbers stamped in to the filter, same steel tube inside,same weight etc. the mobile one filter is usually a few dollars cheaper
I personally dont care about cost. its cheap insurance to run good oil and a good filter and change it out before it needs it. $50 every three months thats only $200/year or $0.55 per day I use that much in gas just warming my truck up