Buying tanks really isn't economically worthwhile unless you dive a lot. Around here you can rent for $6 and fill for $5. So you only save a dollar a dive, which for some people is offset by the cost of VIP and hydro.
But, and this is a really big but, you are paying for convenience. All of you renters have no idea how convenient it is to own your own tanks. Once you own everything, you don't need a dive shop to go diving. Just load up your crap and go. If the weather turns crappy, then you can cancel without wasting a rental. If you get a wild hair andwant to go diving at 3AM on a Sunday morning, then just go. Actually, I hate diving with friends who don't own their tanks because it's such a PITA to get to an open dive shop sometimes.
Once you own, the only time you need a dive shop is to get a fill once your tank is empty. And you have all week to deal with that.
Get the dry suit and a couple used AL-80s. Trust me, you will be glad you did.