If you use LiveVoice for example for simultaneous interpretation, you will probably use it with a combined headphone/microphone set. You can get these for a very affordable price at any tech store.
We can recommend for example these Jabra Headphones.
Or if you want it even cheaper, you can get some for about 25 Dollars like these.
You can even simply use your standard smartphone headphones.
If you use a computer with separate audio in- and out-put, you could get some like these here.