2 of them
The cheapest one is a lotion (permethrine) which you have to put on your body from neck to toes.
It will kill the parasite but won't stop the itching until 2-3 weeks later. The other one is a pill you have to take. Same as the other one, it won't stop the itching. You need another medication for it. Wash all the bed linen and the clothes you were wearing in hot water to avoid reinfestation.