Gerard is right. you'll find one. within the last year, i sold 2, both for under half what 'your' guy wants. the problem with those early tanks, they use the short neck fuel tap which is a somewhat perishable and easily disposed of part. after you've contrasted appearances of a short neck tap on a 19 or early 17 liter tank the later long neck taps don't look right on the aforementioned early tanks.
the early 17 liter tank is also known as the "double wrinkle," it has very pronounced wrinkles on sides of tunnel as well as the usual top. most sellers don't know about this early version, so once in a while they come up priced at late 17 type prices. i know these early tanks have brought $900 - $1100. now that i have written this, i suppose all the ebay seller/lurkers will again be quoting the information they glean off this forum. maybe hermann doering 'sandguss' will magically list an early 17 tank for $10,000 to go with his original 28 caps charade.