I think they are about $10-12 on Amazon.
You can use any magnet [like used in automotive] but then you have the metal down in your juice…I wouldn’t do it.
The lab quality retrievers are coated.
Don’t be fooled by the price of the stirrers, they are not created equal. A quality magnetic stirrer uses rare earth magnets, and the high end stir bars use metal more compatible with the magnets. The shape of the bar is also important, as is the container you use. I make a lot of oil blends, and many are as thick as max VG. It takes me sometimes two or three stir bars to get it where I want it. I have been using these for 50+ yrs, and there is a formula in the lab for what is used, and normally for thinner liquids. If you make the exact same thing all the time, it’s easy to configure, but still make take a handful of components to achieve your goal. Erlenmeyer flasks are usually a ‘gimme’ that they will work, whereas cheap beakers on Amazon are hit and miss for this stirring application. E-juice is new to this method, and so is the info for use. But the viscosity of e-juice is nothing new. Think all the lab testing done on motor oils, and for how long. Good lab equipment makes a huge difference, and many new e-juice alchemists just don’t have the funds to spread around for all the tools they want. I,too, am frugal, but some items require the expenditure. Some of my local ‘alchemists’ attempt their stirring in the storage bottles, like boston rounds with droppers, and continually complain about stuff. They have the small stir bars,a coated bar retriever, an expensive magnetic stirrer, then bitch when it doesn’t work right. The cheap storage bottles have concave bottoms, convex from the opposite angle…BUT NOT FLAT. They want an all-in-one world for simplicity/speed, but end up pissing in the wind from just one small detail. Hate to just ramble, but certain particulars can make this DIY enjoyable…or frustrating. I am just attempting to help, especially with good folks just starting out, and bypass the frustrating part. Sometimes you just have to buy the better quality stuff in key areas, and in the long run, it will be cheaper, and much more rewarding. Sorry for the friggin book, but I don’t know how else to explain it.