Can I make primer from student grade acrylics?
In short: No, you cannot make an effective primer out of paint.

Primer is not just "paint without pigment," and the purpose of it isn't as a base coat; the purpose of primer is to prepare your surface to accept your paint. Some surfaces are too porous to take paint properly (wood, masonry), other may have issues with the paint adhering properly (plastic, metal). By using a primer designed for that specific surface, you alter the surface to allow your paint to adhere properly.

When painting miniatures, a spray primer designed for miniatures of your type (plastic, metal, or resin) will give you the best results, as it is able to be easily applied to small areas without reducing or masking detail. Note that you should in fact be using a miniature primer, as many general purpose primers will "fill in" fine detail areas. There are a number of companies that produce supplies for miniature painting; these will be your best bets for purchasing a suitable primer. If you purchase from one of their retail stores, they can also answer questions for you about how best to use their products; if you are unable to purchase them in-store, I have also found their customer service people to be responsive and helpful via email.

You may be able to find a brush-on primer that will work, but you will likely end up with a thicker base coat that may reduce your detail; you'll want to practice with it until you can use a light enough touch. You will not be able to "make primer" that will be effective in any way; in this case, you do need the right tool for the job.