This is all true. In most instances, the DJ rarely actually received $150 or even $100 per hour for their total time involved in a DJ job. BUT, it takes typically charging about $150 per hour in order to earn around $50 per hour for total time. A 4 hour job is NEVER a 4 hour total time investment for a DJ. In rare instances where there was no prep work, and the event was down the street from where a DJ lives, it might be a 7 hour total time investment, but generally speaking there is at least 6 hours of time invested PLUS the time involved from start time of event until the end time of the event. A 5 hour event is rarely going to be less than 11 hours total, and a 6 hour event is rarely going to be less than 12 bours total.
I would say the band comparison really depends on the type and style of band you are comparing Mobile DJs to. In the DC area, for a wedding, a good 5 piece band is generally going to cost over $5,000. A DJ could be had for as low as $395 for a 5 star rated DJ off of Thumbtack with a whole lot of DJs charging between $600 and $2,500. Even the $2,500 DJ is going to cost half as much as a good 5 piece band.
There are some 4 peiee bar bands that will do bar nights for $350 to $600 a night, but even those bands, if anyone asks them to do a wedding...they will generally either decline it because they don't do weddings, or their price goes to $3,000+ to be willing to do it just because it is a wedding and they know they can charge a lot more than what they get at the bars. There are some 6 to 9 piece bands with dancers that charge $10,000+ through a talent agency to do a wedding now. They don't get booked often, but when they do the clients pay big bucks. I'm just saying, DJs are still generally cheaper than the bands are. DJs just earn more money in comparison to a single band member though.
I think you are proving my point. Far too many variables. Charge what your market will bear, and what you can get that keeps you working.
GJ