Just my musings on the subject...
When the Internet was relatively much newer, and I used to write copy for new websites, a lot of aspiring writers of such copy would email me to ask me how much they should charge (of course, they really wanted to know how much I charged--which was information I more than willing to share with them. Why not, I figured, because I know many of them were running or considering running their writing businesses at a loss, and that didn't benefit anyone in the long run.)
Anyway, my formula then, which may be something to consider here, was to sit down and figure out what I needed and felt I deserved to get for a good living wage.
That meant figuring every cost I faced into the equation along with a good profit margin above what I felt my time was worth (at the time, I figured 15% was pretty good--and yes, that was arbitrary, but I was in the driver's seat as I had something at the time that webmasters clamored for--good, clear and concise copy for their sites).
Costs included my time and skill level (again, arbitrary...what
was my time worth?? And how I figured it was by looking at my personal expenses and how much I needed to earn to survive and prosper at the time), the cost of hardware and software (depreciated), electricity, office space, (even child care was figured in)...you know, all those things any business would take into account before setting its bottom-line price.
When I figured out how much I needed to get per hour, I figured out how long a particular piece of copy would take me to create...and then just multiplied it out.
That is how I set my price for freelance copywriting. And it is somewhat how I do it today, as well, for readings.
Yes, you have to take into consideration what the market will bear. Can or should you get more per hour for in-person readings than for online readings? That's something you have to determine for yourself. If you go to a center to give readings, you've got to figure in the cost of transporting yourself there, as well as the extra time it takes you to get there.
Anyway, that's how businesses run businesses. If you look at this as a business, maybe those are things you might want to consider. If this is just a hobby for you, your mileage will vary.