Yeah you are over thinking way too much. In this hobby as you will learn, the deposit is more opportunity cost to acquire the goods. And in most cases to take the view you are suggesting is penny wise and pound foolish.
If you put that deposit in a short term interest Bearing vehicle for six months, you get what..... 30 cents? Miss an iron man mark vi avengers for example cause it sold out in a day at sideshow, you end up paying much more for the figure.
With a deposit you can get piece of mind and if you flex pay as many folks do it allows people to stretch funds more and acquire figures on their terms.....interest free pmt plans aren't a bad thing.
Else save up your cash in the savings account and splurge that 40 cents of interest on your figure all at once and create instant value.