It depends which option you will choose – independent trekking, organized tour, hiring porter and/or guide, season you are planning to go there.
Cheapest option is independent trekking. In this case you need about 10-15$US/day. Bed in guest houses cost about 2-3$US/night and other expenses are for food. But depending on season and the size of group you are travelling with it is possible to negotiate and stay for free, but you must order food in guest house you are staying. This is possible during low or shoulder season when there not so many trekkers in the mountains. Prices in the cities like Kathmandu or Pokhara are much higher. Expect to pay at least 15-30$US per night for double room in guest house or hotel.
For 10-15$US/day you can hire porter if you feel your backpack is too heavy to carry it all the way. Just make sure to hire porter from reputable company. Can’t recommend any as I didn’t use any myself, but I heard stories how porters leave clients in the middle of trek or stealing stuff from backpack they are carrying.
Organized tours are most expensive option as you can expect. Prices starts from 50-100$US/day depending on trek. There are too many companies organizing tours so it is difficult to summarize all services they offer.