How much is shipping from that site? That might eat up most of your savings. Is there a fleet supply warehouse in your area?
I buy most of my parts from Fleet Products. Here are some Wix air filters I recently purchased.
#57750 List $26.70 My cost $8.64 Oops, that's an oil filter
#46761 List $121.65 My cost $39.32
#46766 List $58.75 My cost $18.99
#46553 List $58.98 My cost $19.07
#42253 List $109.62 My cost $35.44
#51602 List $13.32 My cost $4.30
#42126 List $46.50 My cost $15.03
Yeah, the deal there would be to make a list of all the filters you will need to buy over the next year and buy them all at once (just like I buy saw filters, bars, chain and other common supplies). I believe that having a small stock of all your necessary filters encourages better maintenance as well, because you can't use the "I'll pick one up as soon as I get the time" excuse.
I'm going to wait and see what happens with my possible new truck purchase and then I'll make up a list and place an order. The site also has 5% or 15% discounts for volume purchases. As far as shipping costs, those are balanced out by the lack of sales tax.
The other thing I like about Fleet Products, besides the 70% off list price, is the free delivery. If I need a part ASAP, I'll go pick it up (its about 30 minutes away) but if I can wait they'll send it to me within an hour or two.