Ok, I don't think I followed that at all
You sometimes drop them so you have to start a new pair and as a result make that pair last longer? Ok.. Although if it's not dirty where you drop them you can just use cleaning solution to kill bacteria and rinse them very thoroughly with saline water afterwards to remove any specks.
I buy mine from a company in Canada (I think), so I just order a year's worth when I'm low on supplies. It's half price from what I had to pay from the shop here! My biggest expense these days is the cleaning fluid.