Tristan Italian Threads is having another one of their super-amazing sales on 40wt Aurifil thread. The catch with their sales is that they sell a large quantity of assorted colors all at once (35 spools), but the final price comes out to about $2.50 per spool without shipping. Even with shipping, which is from Canada, the prices are still fantastic for Aurifil!
Just to note, I'm in no way affiliated with the company. I just took advantage of one of their door busters in the past and I was very satisfied with the service and product!