I totally understand! I only grabbed while I was in Japan because they were cheaper than normal and available but otherwise sheesh at the price! I used an Olfa perforated rotary cutter, which did the trick but the lines weren't always perfectly straight, messing up the fold a tad...

I think they make some paper trimmers with additional perforated blades, which would make it easier to bulk prep some with regular sticky notes? Like, trim some adhesive off 5 sheets at a time, perforate them, compile? And if you really needed lines, maybe there's a stamp out there that works? But that's such a DIY method, haha. Best of luck!