I'd rather not speculate on what the 'going rate' is but would rather say that someone could list your Hoover bag at a much lower and fair price on eBay or another online auction site. Indeed, not every seller is so greedy as to put an outlandish price on a vintage item that is more functional than it is decorative or valuable (its rarity notwithstanding).
A famous painting, an authentically-signed baseball, or even a White House vacuum cleaner have definite value--but any old vacuum cleaner bag? Let's be sensible. To make a claim that any Model 65 outer bag is worth over $100 is ridiculous. Correspondingly, many Model 65 bags in fair to good condition have been discarded over the years, because their values were deemed low by their owners--and justifiably so (have you ever discarded something old that had no use or value to you but may possibly have been valued by someone else?). Anyway, I don't think we do each other any favors by posting what we think an item's 'going rate' is or should be on this site as it gives sellers an unfair advantage. Furthermore, as many on this site have mentioned, a vintage item's monetary value is what someone is willing to pay for it.
I hope you will be able to find a bag at an equitable price--in fact it is quite possible. If someone doesn't come through for you on Vacuumland consider checking with your local vacuum cleaner stores (trade-ins), garage sales, flea markets, et cetera.