Undercoat Paint

Gesso primer may be relatively expensive. But I have a few cans of white paint household universal undercoat (This is based on oil). Is this an appropriate substitute for gesso primer when applied to hardboard or MDF before making an acrylic?

The short answer is yes, you can use household paint as a sub-layer or "primary" instead of gesso, especially if you do the work that is not destined to last long, as the students' work studies or art. However, there are some things you should consider.
Firstly that the painting of households, even "flat" paint (as opposed to satin, semi-gloss or gloss) is not a tooth that has gesso, which will affect the "feel" of your brush on the canvas. This is not in itself a big problem, you may even like the effect. What is, is the ability of the undercoat to keep the paint as you do and keep it on the web or in your case, counsel. This is not a problem if you are just experimenting with some styles and technique, but if you are painting you want to sell, you can have long-term problems. This leads to the second question:
House painting is not meant to last forever, there is no archive. Most paints you buy in the shops of art, oil, acrylic, etc. (other than the cheapest paint Student Level) is archival, meaning it is meant to last generations, holds its color, and do not fall under normal conditions of observation. Have you ever seen a Monet or Van Gogh painting?, They could be 150 years or more, and yet the colors are vibrant. This painting archives, and their base is ALSO Archives.
To the point, some of the great works of David Hockney, Jackson Pollock, Mark Rothko, Franz Kline and are literally disintegrating because they used the lower quality paint, and in the case of the Pollock and Kline culprit was ... HOUSEPAINT.

Hope that helps. Keep the paint with anything that prevents you from painting, even a painting of disaggregation is better than no paint at all.

No, I do not think it is appropriate for oil paint has a cure rate slower than acrylic.
You can get a crackling touch. It would not be stable. An acrylic painting would
a better bet.