Actually, I think it does matter how many days you plan on using the gear. If rental for the full set is 45/day, and it costs 180 to ship, well, that would be 4 days worth of rental gear. If you're only going to dive one day, it's obviously more cost effective to rent. If you're going to dive 5 days, then definitely ship if you can get a reliable shipper. Unless you want to factor the intangibles like "it's your stuff" then rent the stuff up to about 4 days worth of diving. If it's only 25 for the extra bag, well that's one way, so it's 50 for both ways, so I generally would take my gear for the extra 5 bucks unless it was going to be a huge hassle.