Estimate conference attendance cost.
Registration is usually the smallest part of attending a conference. Accommodation scales with nights and headcount, travel is a per-person return cost, and meals accrue over days on the ground — which is nights plus one, since you eat on both the arrival and departure days. Splitting the total into those three blocks is what makes the trade-offs visible: cutting a night saves more than most early-bird registration discounts, and sending one fewer person saves the whole per-attendee figure.
Per-person costs
Travel and meals = (return travel + daily meals x (nights + 1)) x attendees
Total
Total = registration x attendees + nights x hotel x attendees + travel and meals
Rarely. It typically saves 15 to 25 percent of the registration fee, while booking accommodation early or sharing rooms often saves more in absolute terms because accommodation is usually the larger line.
For a business case, yes — three days of a salaried person's time usually exceeds the cash cost. This calculation covers cash outlay only.