When it comes to any recipe which calls for the use of butter or a butter substitute I shall probably always refer to it as butter, but you can use whatever butter substitute you prefer. If I think you really need to use butter for the flavour I will say so but feel free to ignore that advice.
One other thing about butter - don't use butter on its own for frying (i.e browning chicken breasts) as it burns very quickly and will really impair the flavour of what you are cooking. Either use your butter substitute, having checked first that it is suitable for the purpose - many of them are not - or use a little butter as it give the nice brown colour, and add a little oil with it.
On student budgets, butter is not going to be a staple item in your fridge, but keep your eyes open for special offers and reduced items for an occasional treat.