A deluxe unit is worth the extra cost for a three-day family reunion because it provides significantly more comfort. The flushing toilet and integrated sink with running water make the experience much closer to a permanent restroom, which is a major benefit for an event with older relatives and children. A standard unit will function fine, but the basic setup can feel less comfortable over multiple days.
For 80 people over three days with food and alcohol, you will need more than the minimum number of units. A common planning guideline starts at about one unit per 50 to 75 people for a four-hour event, but longer duration and alcohol consumption mean you should add units. Plan for a small cluster, perhaps three or four units.
You do need an ADA-compliant unit if you are placing a cluster of portable toilets at a single location. The 2010 ADA Standards require that at least 5 percent of the units in a cluster (which in practice means at least one) must be accessible. This unit provides the required turning space, grab bars, and appropriate door hardware.
The price difference is driven by the unit's features. A deluxe unit costs more to rent because it has a flushing mechanism and a sink. Since your event is three days long, you will need at least one mid-event service visit to maintain cleanliness, which adds to the total cost. Good truck access simplifies service.