I am shocked by your advice.
The 3090 video card is shit in mining for a beginner. This video card is expensive and it heats up. If you were an experienced miner, then the purchase is possible, but not for a beginner.
If you have free electricity, then you need to find a miner with video cards and divide the profit by 50% each.
You do not have risks and you do not need to spend money, and if you have extra money, then it is better to invest in cryptocurrency.
Finding a miner now will not be a big problem.

These people who made this listings don’t really think straight. They put stuff like “you can make up to $100/day”, etc, etc.

They list their home address for pickup, and they don’t worry that they will come back and demand a refund?

I think that the ones who are doing this were the ones who bought GPUs in early 2022 and they are sitting at a loss and want to recoup their losses.

Most people I know who are new to mining they all funded their gear with credit cards which charge 20% interest.

It is better buy coins.for 7-8k you will get good amount of coins at these prices. Or 50/50 for half money gpu and half money coins if you want mine so badly.back to your question rx5700s and rtx3060 are good options to start