If you are planning to buy a fair amount of AMSOIL and other AMSOIL products, I found it was worthwhile to go to their website, AMSOIL.com, and join as a 'preferred customer' . I just joined a few weeks ago @ $10/6 months. I more than got my 'club dues' back on my first order. You will get ~15% off the retail prices quoted on the website (and the $6 you quoted for oil...and I'm assuming it is diesel oil... sounds roughly like the retail price).
I am transferring everything to AMSOIL oil and filters, so I will be purchasing a fair amount over the next several months as spring tune-up time is just around the corner here in the deep south.
Check out the website prices, calculate what 15% discount comes to, and compare to the $10 'club fee' to see if it makes sense for you.
RET