If you are a costco member they can have some sweet deals on rentals (2nd driver free) but if you are coming out here a couple times a year it might make more sense to buy. also depends when you are coming over. if always xmas spring break and summer then rentals will always be $$. If coming over when kids are in school usually cheaper. If buying then do you buy kauai or mainland and ship? kinda depends where you are at. westcoast and close to ports? mainland probably cheaper and more selection but you have to factor cost to ship and it might take a while. I know oahu was backed up shipping outer islands for a couple months don't think its gotten much better. call and find out. 4x4 would be nice if i was southshore to cruise polihale and when weather is junk its good to have that feature on kauai. browse craigslist and get a feel for prices, anything toyota or a truck will hold value if you bring over mainland. I had a similar deal where I used to keep a beater truck over on lana'i when i would go hunt a couple times a year but I kinda got over having to worry about maintenance, safety check ,extra cost insurance, never know when its gonna break down etc. ended up getting rid of it and just renting now because its way less of a hassle when things would go wrong. For that reason I would budget at least 5k (prices may have gone up though last i rly was looking a vehicles was a year ago), so you can get something somewhat dependable. I think there's a pretty active kauai buy sell facebook group too in addition to craigslist.