As my great-grandfather used to say about horses, it's worth what any damn fool will pay for it. Antique vacuum cleaners are such a niche market that any assignment of value is subjective at best. A collector will see considerably greater value in it than the average person, who will likely see it is worthless junk. Probably the best way to gauge its value is to find one like it, or preferably more than one, that has sold on eBay, but bear in mind that eBay prices are often inflated well beyond that of a private party sale.