As I mentioned in my post about requests you can make during job negotiations, one of the best things you can have when trying to value your own skills is to look for similar examples from your colleagues. This is the crux of salary transparency: being open about what you've been able to get makes it harder for employers to underpay workers. Nowhere is this more important than grad school, where even a little job here and there can make a huge difference in your monthly financial plans.
Historians of science in particular will either bristle with frustration or joy at the prospect of quantifying your work. Hourly rates are bananas and can fluctuate wildly depending on who's asking (and what you need). Having a rate sheet can be really helpful -- here is the sliding scale rate sheet that a friend of mine uses for organizational coaching and facilitation; he also has a separate one for individual coaching, which you could adapt for consulting. For whatever reason the people I know who are the most transparent about their pricing are those who work on coaching / resume / etc services — which is probably not your jam at all — but I think the way that they package their services is really interesting. It's also helpful to keep in mind that you may want to bake in the time that it takes for you to do some of the associated admin work, including chasing after invoices. Wudan Yan and Jenni Gritters' "The Writers Co-op" podcast has a wealth of resources related to this, and I found Wudan's post on trying to collect late fees to be especially instructive.
Here is another example from someone I knew in college. I like Brianne’s because she is very clear about what each package does and doesn’t include, and asks clients to come prepared so that everyone walks away from the meeting with the most value.
Those are primarily for projects with report-like deliverables, which is different from speaking. I've found Tatiana Mac's speaker rider to be a fantastic template to build on for non-academic events, and gives you a sense for what you might be able to ask for that's not money (and what you should absolutely be getting, like travel / conference fees covered at minimum).
Now to actually getting the money: if you don't have an invoicing system, I use a free invoice generator for one-offs. If you want something more sophisticated, particularly with time tracking, I love TopTracker (not sponsored). I often use it to track how much I work on academic / service stuff too (even without the invoicing etc functions), and it does stuff that a lot of freelance contracts like by keeping track of screenshots and such.
Hope this helps!