You could always ask them to wait?
I say this often, but if it is a hobby then you do as much as you can afford - if that is once a month or once a week or every day. If you loved going to the cinema, you wouldn't try to make money from it just because you wanted to go more often than you could afford, rather you'd go as often as you could afford to do so.
If someone wants something big specific then asking them to pay for the ingredients for the batch is one thing, but that isn't going in to business. As for the time, if you don't enjoy soaping enough to make it that often, then maybe telling people to wait a few weeks is in order.
You don't HAVE to monetize a hobby - hobbies do cost money and time.
It's not so much that I mind it turning into a business. It just sort of turned faster than I had planned and I learned the hard way that I need to keep my head above water. Come this fall, I will have to tell people to wait though (I'm not throwing away a past year of grad courses).
In the mean time, I still do enjoy it which is why I have a hard time really considering it a "business." However, when I spend 6+ hours literally every evening making product just to keep up with requests, my time has a monetary value as well, beyond just covering products. Anyone that's gone full force at anything knows there is a time value for money.
Right now I consider it to be walking a very fine line between hobby and business for me, but given that as of two months ago I've been getting significant requests from non-friends/family, I did have to foot the cost for insurance too (wow was that a brutal expense). I don't really want to come across the one random, disgruntled person that destroys everything I've built.
As for hobbies costing money, I'm all too familiar with that

I used to breed seahorses for research/conservation studies, I spent 3 years racing a cobra, and only recently did I sell my jeep trail rig (by far the most expensive hobby!!!). From a hobby perspective, this is easily the most affordable one.
I'll tell you what though, this forum has been a blessing! For ages I was making soap from a single family recipe that was around 100+ yrs old. I had no idea soap could be made with colorants, fragrances, etc and be made to look so pretty. And you guys are a fabulous resource with endless info (and the occasional laugh that gets me caught at work reading the boards)!