For each child in a car seat, how many do you have? Also are they the same price range? Or of varying price based on amount of use?

I have a 4-Ever-All-in-1 in my car, my husband has a Nautalist, the babysitter has an Extend2Fit.

I'm considering getting one for my sister's truck so she can pick him up 2x a week since she works close to the sitters house (which he's at twice a week). And I'm torn on what seat to get him. Like is it necessary to spend a couple hundred dollars on a carseat that might but be used past July (when her lease is up and might not live down the road from me anymore) or if there are cheaper but just as good? Like, I don't want to skimp on safety, but don't want to waste money on one that might not get a ton of use.