fDonovan,
Playing devil's advocate ... do you have a habit of returning items to the store, and/or were you in any way rude to the manager (if so, apologize and tell her you'd appreciate her willingness to negotiate)? While there are some individuals that are just plain difficult, often one is treated by others how s/he communicates with them.
Regarding the store's price, consider first of all that those who don't collect vacuum cleaners, likely including the manager, have limited knowledge about them. The rust, lack of original attachments and the users guide would make the cleaner less appealing to many collectors but not to such persons.
The monetary value of old personal-use items (distinguished from famous or extremely rare pieces) is relative to each person's preferences. For example, a vacuum cleaner collector who favors Hoovers would not pay as much for an Electrolux as an Electrolux collector; and even Electrolux collectors differ in their individual tastes—some preferring such details as features or decade styling, design, particular model numbers or model names, et cetera. For a non-collector old vacuum cleaners belong in the trash or in a rummage sale at a nominal price. So, the old adage holds true, "Beauty is in the eye of the beholder".
As for the term 'antique', there is no universal definition among sellers and collectors, but it typically refers to an item around 100 years old. Other general age-related collector terms are Depression-Era—1930s; Mid-Century/Retro/Post WWII—1940s & 1950s; Vintage/Vietnam-Era—1960s & 1970s; & Classic/Early Electronics-Era—1980s & 1990s.
Btw, the Electrolux cleaner you photographed is a Model E_Automatic, that was manufactured between 1956 and 1957. You will see the identification tag on a metal plate near the caster (the serial number—a 5-digit production number between a 2-letter series is also on the tag). There was also an earlier non-automatic Model E, made from 1954 to 1956; that is similar-looking but has a removable bag door, wheels/stabilizer, and handle assembly/switch.
In your case, the fact that you haven't seen another Electrolux cleaner for sale in your area should definitely influence your decision to buy. Also think about the fact that older Electrolux cleaners are typically able to be refurbished to new or near new condition with reasonable time and effort.
Keep us posted.
