hey bro good luck for your marriage. i was there in nepal in last summer and attained many marriage ceromony. and my brother marrige ceromony too. these days in nepal , most of the party are organized in party mall, or party palace. and u will find so many these days in nepal. the actual cost of the party depends on the per person. the cheapest cost u will find is Nrs 450 to 500  per person. and the expensive goes to NRS 700 to 800 person. and its up to u what kind of food u like to have. and this price includes the cost of the party palace itself. so if u are inviting 500 people. the total cost would be multiply per person cost to the no of people.and

secondly. excluding food , u will have to buy your own cold drinks, beer and wine. its up to u how much u want to keep in the party, normally the party palace where u hire, they can provide all those cold drinks , beer and wine, but if they provide for u , it will be too costly. its better to buy all those drinks from outside and ask the party palace manager. 

third about the band . i my frends wedding we played  a live band in the party. so we just hired the sound system, and spend about 8000 nepalese rupees. and if u need some live band in the party. they charge around Nrs 20,000 . it up to u how u bargain. 

finally if u need a band for the janti , i don't know exactly, i heard that its cost like Nrs 30,000. but i am not sure abt this wedding band