It depends on the event. The bigger and more prestigious the event, the more they will pay. This will range very widely from $0 - $1500 and up.
Whether the event will want to hire your band for that price depends on a number of factors, least in importantly of which is how good you guys are (lolz). The important factor is how well known your band is - if anybody organising the event knows of you, or if they can find you on the internet. Of course, being good typically means you'll be more popular and well known and thus will be higher in demand.
As a rough gauge:
Charity events: $0
Events organised by students: $100-200
Small public events: $200-400
Larger scale event: $depends how much money the organiser has in his budget. I've heard in the past that EIC could easily get $1500. Hearsay only though so don't quote me on that.
Acoustic vs Full band: As far as i know, most organisers don't really differentiate between the two.