How much money does it cost you to create that node?
Can I use my PC (CORE i7) to do this, or do I need a specialized hardware device?
You can use your PC with i7 CPU, but cheap/low-power PC such as Raspberry Pi is good enough.
I read on one of the forums that I can make returns from $ 10 to $ 30 a month?
If this is true and I can manage 3 nodes without having to sit in front of the computer for a long time, then perhaps it is considered a good source of income in some countries where there is electricity and equipment.
Money you earn depends on how many transaction is routed through your node and routing fee that you set. I doubt regular user could earn $10 - $30 / month only from routing fee.
But based on your question, i think you don't understand about LN. I suggest you research about LN and how it works in general.