When all you have is a hammer, all your problems look like nails.
What I mean is that once you have the means to reach high places, all manner of uses seem to come up. Let's look at ways to do 'high work.'
You can let someone else do it. For example, this is the sort of thing sign companies do all the time.
Some guys make do with scaffolding, but I consider that far more trouble than its' worth.
"Owning" the means for high work isn't really much of an option, unless you specialise in a particular sort of work. There are just too many limitations on what you can do with each sort of equipment. Let's look at some of the different ways:
Platform lifts like the 'little Genie' can work, but can easily become unstable. Their 'big brother,' the scissors lift, can't handle much deviation from a perfectly level surface, and are limited in their soft-ground abilities. While you can tow the smaller ones, you also need a trailer. Apart from the rental cost of the trailer, getting the lift back on the trailer can be a challenge. Still, doing your own hauling can help you get the most out of the rental.
Towable booms are great, but have quite a footprint. I usually line up several jobs and work a LONG day whenever I have to rent a towable boom, just to spread the expense around.
Self-propelled booms are nice, but you can't tow them with anything less than a 2-ton truck. You're now in CDL territory.
If you're working indoors, you might want to invest in a basket for working from a forklift. The expense is minimal, and the convenience great. Customer provides the forklift, and maybe the driver too.
For your particular application, it looks like a towable boom is the best bet. I'd try to line up other jobs - gas station lighting is a good source, as are apartment complex / shopping center parking lots lights - and schedule them together.
As for rental sources .... sure, HD is a good place, but the 'real' rental houses will work with a regular customer, and take some of the sting out of the rates.