A GoPro Hero might weigh 150 grams with the protective case. A Hero Session weighs half that. On a static KAP rig the total weight will be 150g to 300g. Let's say 200 grams.
Braided Dacron 200 lb test line weighs 250 grams for 100 meters. Lighter line can be used, but you might want to fly higher. Let's say 250 grams for the line.
To lift 450 grams you need 450 liters of helium, but you really want more than the minimum, so let's say 600 liters or 20 cubic feet.
You can rent a 40 cubic foot tank of helium for about $50. That might be good for two fillings which will lift 450 grams. It depends on whether the helium you buy is pure or mixed with some air.
With some balloons the helium does not leak out very fast so you can use the same balloon for many days and maybe top it off with more helium if some leaks out. So the helium could cost as little as a few dollars per flight if you make a lot of flights over a few days. But if you only want to make one flight, it costs you $50.
Chloroprene balloons can be filled only 4-6 times before they degrade and become vulnerable to popping. So the $30 to $60 cost of the balloon must be amortized over several flights. Let's say $10 per flight.
So the expendables for helium ballooning are maybe $20 to $60 per flight.
The expendables for a drone can be low if you don't crash. But if go that route, you might be buying extra batteries, spare props, and other toys all the time. Even if you don't crash (and you will) it costs $500 for a new fancier drone every couple of years. A drone can make a lot of flights before it gets replaced with a new drone, so cost per flight can be low. But flights are only 20 minutes long, compared to endless balloon flights. And if you don't make as many flights as you thought you would, cost per flight cannot be ignored.
But regardless, you're going to buy a drone, aren't you?
Chris
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Thank you cfastie for your input. I invested in two new kites. I have not tried solar or balloon photography, but I'm looking forward to it. I have not purchase a drone, yet. I'll keep you posted.
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@cfastie mentions the most pernicious fact of flying-- once you start collecting equipment you might never stop. That's true for whichever method you choose.
While I enthusiastically endorse the sheer delight of flying solar balloons, they are an impractical way to take low-altitude photos. They also have to be too big for tethered flights above 100' or so.
At this point drones are a great deal, especially with built in cameras. Multicopters, however, are aimed at video-making and low-altitude oblique photography. Most inexpensive ones don't have much stamina for mapping missions. When multicopters crash, they crash hard and break parts.
Consider a fixed-wing. Although less mass-market and with fewer out-of-the-box options, I think fixed wings are a less expensive platform long-term. Batteries R/C equipment can be swapped and cannibalized between new foam bodies that are cheap.
Fixed wings also lift more for a given weight. You might even be able to put a small camera on one of the 250g models that don't need registration.
Many fixed wings come with crash-resistant foam bodies. Styrene foams EPS and XPS are good for wings but crack in crashes, while EPO/EPE/EPP are nearly indestructable (think pool noodle).
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Adding another idea, perhaps a solar balloon https://publiclab.org/tag/solar-balloon might be interesting for your use case? @mathew makes these, for instance, and i have flown some of his and also some by @AeroceneFoundation
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