How to lazy mint your 10000 nfts on erc721 smart contract and display into opensea?

Hi OpenZeppelin community ,
I am new baby in blockchain , I have question that is there is any way that I can lazy mint my bulk nfts to erc721 smart contract and then display them in opensea .

Or there is any other method by which I can mint the bulk nfts paying in small fraction.
I met a guy , he is saying that he will mint my 5000 nfts in just 1000 usd on erc721 doing minting , how he is doing that ?

Thanks in advance for your help !