At many dive locations you can just rent tanks for the day. Breakwater at Monterey is an example.
What you probably can't rent is a tank for Nitrox. If you want to dive Nitrox then you will very likely have to buy your own tanks. Then too, you can't get clean (Nitrox grade) air at Breakwater either. So, you have to bring enough tanks so you don't have to refill or you have to cart them a few blocks (and lose your parking place) to get them filled.
So, I have 6 HP 100s for the 3 adults and 5 Al 50s for the grandson plus a steel 72. Right now the 50s and the 72 are seeing some serious swimming pool duty. I really like the 72. I intend to buy some more.
The son-in-law and my wife are taking a couple of specialties in Tahoe in the near future. We still wind up renting 4 tanks so we can come up with enough for the 12 dives (total), 6 of which will be Al 80s with air.. Otherwise, we have to fill with dirty (not Nitrox grade) air and I don't want to have to reclean my Nitrox tanks.
We really need another 6 HP 100s - about $2100 ought to cover it. Or maybe 4 more Al 80s for about $600. We'll see.
Richard