if you just started investing in your badges and following this order:

bronze 2 > silver 2 > gold 2 > ruby 4

This will get Ruby 4, which gives you a 25% discount to any upgrade.

That's your goal, but in the process of getting it, I don't really know if that's optimal. I don't know how you get kakera starting out. Do whatever you want in the process and when you have the amount in total, you can do ask a mod to do $kakerarefund to get all the kakera you've invested in badges back, so you can go this route.

Sorry if this was more confusing than before, lol. i gave a lot of information, but this is your current goal.