My opinion is that you have a better bet getting your own bike, and having a biker friend or someone take you for some lessons. In that way, you get the feel of your own bike, while getting lessons on control and balance and so forth. Sure, they might then teach you all the wrong things, according to the K53 method, but they'll teach you how to survive on the streets, which I feel it's more important.
Also remember that K53, whether in a car or on 2 wheels, is more a guide as to what to do, and how to do it than actual gospel as some instructors might tell you. Even freshly passed out drivers soon forget 90% of the K53 lessons when they really start blending in with road traffic.
In my case, I'm riding for a month and a half, I basically taught myself how to ride a bike, and manage traffic. From watching countless Youtube videos, and actually taking note of what they were saying, I was able to within days begin riding in peak hour traffic and being comfortable on the road. All this with my own bike, so pressure was on not to drop or crash the bike. Now I know not everyone will be as mad as I am to do it that way, but I thought I'm going to be my best teacher, I best learn my own style from the beginning, and with the help from friends, work my way around the challenge. Some might find going to a riding school the best option, but that's perfectly acceptable. I'll give myself another month or so on the roads before I book for my drivers test and get info on K53 classes.
You said your mom gave you the ultimatum to do lessons in order to get a bike, well, then best shop around for lessons. I'm not too clued up in the Gauteng region on that, I'm from the flat mountain crew. There must be places that's under R1000 for beginners classes, including the bike hire for the session. Here in Cape Town, there's a guy that charges R600 for a 5 hour course on beginners, including bike and helmet hire. So shop around, make phone calls, check the Think Bike website, there might be info there too.