Buying NFT (on Polygon) on OpenSea programmatically using web3j

I need a code piece in Java that can programmatically buy an NFT that is minted on Polygon on OpenSea.

You need to use web3j java library. You can use Infura as the eth node provider.

Your code should interact with the OpenSea marketplace smart contract, pay the price and transfer the targeted NFT to your wallet address.

The code should create this kind of transaction on the chain..

https://polygonscan.com/tx/0x6c812bd8580d3470d2be287b836cdafbdb7f4378bb0d5fa7da62aef5899fd45e

I want to run this code on my Java backend so you need to be able to sign the transaction on the backend in the java code, NOT using MetaMask.

If this is not possible to do in Java, I am also interested in buying this piece of code in JavaScript (Node.js)

Please give me a quote and duration for this task.

Thank you.