They can be expensive or cheap, and the cost depends totally upon one's interest in spending. A few factors affect the most, such as the number of guests, venue, food, entertainment, etc., and these things make it a bit difficult to give the exact price. Mostly, don’t think about show-offs. Consider your budget as well. Thus, do what works best for you. And if we talk about paying, traditionally parents have to pay for the party, but nowadays couples themselves pay for it.