Last time i saved money by buying via local distributors.
Did you check through other local MMO style merchants? LIke Paysafecard? I used to buy through Molpoints (karmacoins, paybysafe, google, paypal) as they got better rates for some regions.
I think steam, and warframes main distributor who sets up transactions on their websites have increased their markup. I've noticed this across the web in the past year where allot of prices have risen.