Wow. Totally diff mindset here. 865 for OW class is crazy. 250 here. Ive always owned my tanks. We typically carry 3 to 4 tanks per dive when we go deep or have 3 to 4 tanks pp when we go out for the day. Rentals here are 8 to 10 per tank per day depending on which LDS so rentals are unrealistic for the long term. Even the most expensive doubles set i ever bought was only 400 used. 480 total with hydro/vip. At 120 to 160 a month for rentals those tanks pay off real quick. Try several different tanks and see what you like or works best for you. Honestly aluminum 80 rental tanks SUCK. crappy boyancy swing and low volume with no option to overfill. A lp steel 80 is a much better option. No need for extra weight in most situations. Smaller tank. At 50% overfill it becomes a 120. Personally never push mine more then 50% over but i know a few that do. To each there own. Dont know were your at but you may want to check class prices in FL. Get certified in the warm water and sunshine for alot less then 865 and take a vacation at the same time.