BMW only sold the R6 in 1937 with a total production of roughly 1,850 units. It was the follow-up to the legendary R5 (one of the styling inspirations for the R18) and their first 600cc motorcycle.
The side valve boxer engine displaced 594cc, good for 18 horsepower and a top speed of about 75 miles per hour. BMW marketed this as more of a touring rig than the R5, and many equipped with sidecars. For more on what Motorcycle Classics calls a “one year wonder,” check out this story (though it now looks like you have to be a paid subscriber to read their articles so I may unfortunately be moving away from using Motorcycle Classics as a reference in the future).
This example has a hefty 89k miles on it but there isn’t much provided beyond that in terms of details. The seller of this is the dealership MAX BMW (they’ve been a great resource for me for parts over the years). It’s listed on their site for $85k and on eBay for $80k. I really have no idea what these are worth but Mike Dunn of Vintage German Motorcycles is selling a restored example for $45k on his site.
Find this R6 for sale in Troy, New York with an unmet opening bid of $80,000 here on eBay.