Is developing a cheaper method ever considered to be originality in academic research?
What are the necessary conditions, if any, that allow X and Y to be published as a journal paper?


That the method or equipment is new and interesting. It is really as simple as that.

It is completely ok if the improvement or motivation of your technique mostly lies in cost savings - that is common in many research communities. If the way how you achieved these cost savings is by applying simple technical optimisations, you will have problems publishing your results. On the other hand, if you reduced costs by fundamentally changing the way how your technique approaches things, or if you manage to reduce costs by orders of magnitude, journals will presumably be interested in how you achieved these results.