Ask the shop to take some off the price, and pay with cash. Local shop I go to, I tell the guy what I want to pay, and he tells me if that's possible. Usually, it is, especially if I'm paying with cash.
And keep an eye out, especially on thedecostop.com for steel tanks. You can find good deals. I personally found aluminum 100's two years into original hydro, with current (done when I bought them) vip, for $125 a piece. That's less than the price of a new 80, and many places "new" is one or two years into original hydro date.
You can find deals on steels on TDS, prices there are better than on SB. Ebay is never a good place to go. Never pay what the person asks for on Craigslist. If they want $100, offer $75. If they want $300, offer $250. Argue your point: tell them it'll cost $30 to get it hydroed, you can use this very effectively if it is out of hydro or near the end of the last hydro, tell them it'll be $15 for a vip, which is useful if it's out or nearly out of vip. Take $10 or so off for every hydro stamp, if you can. Basically, bargain with the guy, but try to point out why your value, what you want to pay, is more correct than the asking price.
And if you are selling things, you do the opposite: point out why your price is more accurate than what the buyer wants to pay
Know what you are selling, know prices, be able to quote them. I rarely sell things for much less than I ask, becuase I'm very good at arguing why my price is right. I rarely pay what people ask, because I'm very good at arguing why their price is wrong.
Case in point: I'm buying a $100 truck topper for $75, and all I had to agree to was to go pick it up. And the guy even thanked me for taking it off his hands!
Two months ago, I listed some regs for $150, and the buyer wanted me to take $100. I pointed out that the service, done 6 months before, was $99.95, and that since then I had replaced three hoses, at $15 each. I paid $145 just to get the regs in operating condition, and only had two dives on them. I let him breathe through them off of a tank, and tossed in another mouthpiece, and he paid me $150. I would have sold them for $130 but was able to get him to pay what I really wanted by knowing my numbers. Then again, I wanted to sell a guitar for $150. Buyer drove two hours to meet me, he offered $120. I knew I had him, he'd just driven two hours, I could ask for $150 andhe'd probably pay it. But he knew his guitars and pointedout some flaws which I knew about but didn't want to obcess over, so we settled at $130, and both of us were happy.
So, offer to pay $350 for both tanks. But i wouldn't do it, you canf ind better deals on TDS if you wait and wait for a while.