Alpha Acid Difference...

My next two planned brews call for a good amount of Amarillo hops so I decided I would buy a pound from Farmhouse to save some $.

I normally buy most of my supplies from Midwest but they are currently charging $3.40 per oz for Amarillo hops whereas Farmhouse would work out to $1.54 per oz (including shipping) if I were to buy the full pound.

I did however notice that the alpha acid % in the Midwest hops are 8.2 whereas Farmhouse's Amarillos are only 6.9.

Is this difference a big deal? Will I need to increase my hop additions with the Farmhouse Amarillos?

I am assuming so but I don't have my beersmith software on my work computer and was hoping to order the hops today...

The general rule of thumb is to convert your bittering addition but not your late additions. With that much of a difference in alpha, you'll want to convert.

(Weight of hop 1) * (AA% of hop 1) = (weight of hop 2) * (AA% of hop 2)

Follow what was said above. You might call to verify the % at FBS. I did get some Amarillo last week that was 6.9%.
I also ordered some Cascade that was supposed to be 5.9% and when I got the package it was 4.7%. I didn't order any extra and was not happy. I had to swing by the local shop to pickup some more. And the reason I bought online was to not have to drive to the local shop.
I know that when they get a shipment, the % changes for them and it's hard to keep the site up to date, but as a business, they need to.

Thanks for the advice, sounds like it shouldn't affect me too much if I only have to adjust the bittering hop addition.

It's not a big deal. I bumped up the 60 and 30 min addition but it's just something I tried. Doing the 60 should work just fine also.