Astrum well, I'm just saying that price shouldn't really be the ONLY factor. Look at reactors for example:
Standard reactor: produces 0.375 power/ton/cubic metre
Medium reactor: 0.5 power
Large reactor: 0.84 power
reactor 1x1 (Forge): 1.52 power/ton or 0,38/cu.m
Even without prices, you can see the logic with the vanilla ones: if your ship is large enough to house a bigger reactor, and you're ok with putting more eggs in one basket/provide more defense/allow for optimal distance, you'll be way better off with a larger one, so no need to spam standards. With the 1x1 here though, I would pretty much always prefer spamming it to almost any other alternative. Not only it is simply better in all aspects than the standard reactor - I would almost surely prefer it to the bigger ones as well since its 1/4 of weight per energy generation would allow me to save weight elsewhere and either have my ship be faster or place fewer engines. Same goes for many other parts.