I will give the gntd promo card for each 50 boosters purchased + 15% booster bonus. In your case of wanting exactly 50 you would get the promo card and 8 extra boosters. I round any 0.50+ booster percent upwards. I'll be paying with SPS and am passing the 10% savings to anyone purchasing packs with me. That puts the cost of purchased boosters at $3.60 USD + a voucher.

There's some drawbacks. One that you noted, no future airdrop potential. I won't be making my purchase until the last days of presale / first days of grace period. Presale last 4 weeks and then there's a 7 day grace period in which the presale still takes place but no more vouchers gets airdropped. I will accept HIVE/HBD/DEC or SPS as payment. Payment needs to be given to me before I make my purchase. I won't be accepting payments until the days leading up to my purchase.

Fail safe for your currency while I'm holding it. Once you give me the funds + vouchers to cover the cost of the booster purchase you want I will lock that price in for you. This means that if the value of the tokens used as payment dip, I will cover the extra cost myself BUT if the value of the tokens rise I will send you any balance not needed that is owed to you. This applies up until the moment I make the purchase. I'll likely put out a detailed post within the next 24 hours to see if this gets any interest.