It's cheaper to buy both the game and expansion separately on amazon --> $38.90 + $10.50 (for expansion, this is more rare so prices will vary) = $49.40. Free shipping on amazon for orders over $50, so just throw on something cheap to offset the $50 price.
The massdrop full unlocked price $36.99 + $14.75 shipping = $51.74
Massdrop has lowered their shipping fee = massdrop beats amazon by about $4~$5
The shipping has now been reduced to $8.25
Full unlocked price $36.99 + $8.25 shipping = $45.24
So the tradeoff is if you want the game+expansion in less than a week, you can pay around $50 from Amazon.
Or you can commit to this drop for $45.24 and wait until it ships at the end of the month, which means you'll get it probably beginning of August.