Really, pretty much anything is a good price to fix your tank.
Your options for the M715 are pretty limited: either find a good used tank, which is hard, repair what you have, or go with something entirely different and modify as necessary.
Were it me, I'd clean it really well inside with something like phosphoric acid, then try to remove all of the previous repairs. Fix any damaged areas either by cutting them out and replacing them totally, or spot repair properly with something other than brass brazing. Lastly, coat the inside with a good ethanol resistant coating like Caswells.
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