Wireless power transfer (WPT) transmits electrical energy without physical wires, using electromagnetic fields. It involves generating a time-varying electromagnetic field by a power source, which the receiver then extracts power from. WPT offers advantages like eliminating the need for cables and allowing for more mobile devices.
Read about transformers to learn about power transfer using induction, particularly air-core transformers in this case.
Yes, we know the definition. Do you have a question?
If the question is how do I make one? Then the answer is it a is very small range device and doesn't transfer very much power. Also the device you need to transfer power to, will have to rest on the coil providing the power, or within a few mm of it. You should separate the two using a none conducting plastic.
So we need to know your expectations and how much power you need to transfer.
How much will it cost to get one
All depends on the spec and power requirements.
A pre-made transformer is unlikely to help, but the theory wil help you decide.
Wireless does not mean non-contact power transfer. I have a flashlight that charges wirelessly, but does have a magnet that ensures contact.