craigslist mate, tanks are one of the worst things to buy new due to depreciation.
Have to drive for some. Didn't see any on craigslist near you right now, but if you get in with the cave diving crowd there are usually guys shuttling tanks around pretty regularly and there are some big names in our community up in NYC.
https://washingtondc.craigslist.org/mld/spo/4886931502.html
Those would be worth the drive, they are 120's not 100's, they are the skinny necks so you'd have to negotiate a price with the singles valves since that manifold can not be capped or plugged. Only downfall to those tanks is they have to be used with 300 bar DIN regulators, due to the 3500psi pressure, but they are beautiful tanks and my personal favorite bottles both in sidemount and backmount. They'd fit your size well.
Marketing makes products cheaper yes, but only when the sales of the products are higher pushing the margins lower and cost of the products the same or close enough to oust competition. When the margins are the higher, cost of production is lower, but cost of purchase is the same or higher, you are feeding corporate bloat. DSS makes a higher quality product, in one of the most expensive places to do business in the world, but they keep their prices cheaper than the big boys do. I know how marketing works in the real world, but this industry is so f*cked up the normal rules of business don't apply. If they did, Suunto's new Eon Steel wouldn't cost $1500 when Shearwater puts out a computer that costs about the same to manufacture but have chosen to take a realistic margin on it and not spend hundreds of thousands of dollars marketing the thing, so they charge $850 or whatever it is for it right now, their dealers only make $100-$150 on it, and they sell a boat load of them, the Eon Steel dealers probably make at least $500 on it, but sell fewer of them so it just doesn't work out.
If your statement applied to this, then Scubapros X-Tek would be cheaper than the rest of the market, but instead they choose to spend the money to market it, then price it at or above the competition and don't end up actually selling stuff anymore. Unfortunately in this market there isn't a lot you can do to separate yourself from the other guys with marketing because most of it is coming out of the same 3 factories in Asia, so quality is all the same, it's all on price and little bit on brand loyalty now. Now, in recreational gear marketing may work better than it does in technical diving, but if marketing actually worked to keep prices down in technical diving Hog, Dive Rite, Deep Sea Supply, and Halcyon would all be out of business and we would all be diving Aqualung and Scubapro gear, but with the exception of regulators and jet fins, you don't see much from those two brands, you see the three above because they are cheaper to buy and generally equal or better quality.
If you can give me a single example in technical diving where marketing has actually made a product cheaper I'll eat those words above, but I can't find a single product from Aqualung, AUP, or Scubapro that is cheaper and better made than competition from DSS, Dive Rite, or Hog, none of which have huge corporate structures, or spend huge amounts of money on advertising, Dive Rite more than the other two, but still nowhere near the amount of the first three