Nepal is most famous as the home of half of Mount Everest, and those actually climbing the mountain, or to the main elevated base camp, will have to deal with those not-insignificant expenses. But those just coming to admire the city and its Buddhist culture will find it to be very cheap by international standards.
Prices for hotels and hostels are nearly as cheap as those in smaller cities in India, which are generally the lowest on the planet. It’s worth noting that hotels and guesthouses at the absolute bottom end of the price spectrum will be quite minimalistic, to put it kindly, but paying a bit more gets you something not bad at all. Of course there are now a number of expensive hotel resorts meant for those on much larger budgets, so nearly all price ranges are catered for.
Transportation and attractions in the city are also very cheap by nearly anyone’s standards, so your main expenses will be guided trekking excursions or adventure sports, if you choose to do them. Food and drinks are also very cheap by most standards so this continues to be a great stop for budget-minded travelers as well as those who can afford the best.