A 3.5mm headphone jack has just enough power for the sound volume needed for a headphone. That's not what you are looking for.
I doubt if a USB powered speaker set would be loud enough for you. Try that in a shop. If not, you need speakers with a power adapter. Since your desktop computer is connected to the mains also, I don't think that should be a big problem.
Prices vary from $10 to much higher depending on the output power and quality.
A question about computer speakers
I want to purchase a set, of mini-speakers, for my desk top computer.
I am looking for a product, which is corded, and powered by the desk top computer.
Nothing fancy, or expensive.
Just basic speakers, powered by the computer head phones port.
Where should I look for such a product, and how much should I be prepared to spend?