If you want lower rates, you could check Paxful or LocalBitcoins. If you're okay with 1:1 then use gyft or eGifter.
Buying from online sellers "Paxful or LocalBitcoins", will expose you to buying illegal cards "Stolen/ hacked / not working".
gyft or eGifter: Sometimes cards do not work.
the only properly legit place to get amazon.com cards any more is inside the copay/bitpay wallet. everywhere else and you're dealing with third-party assholes who are probably gonna rape you given the chance.
This is the most acceptable solution. "You will pay a higher fee, but you are dealing with a trusted company with an excellent reputation"