Forgetting the substantial price difference for a moment, there are only two monoculars worth considering.
The sublime Leica Monovid 8x20 or any of the Zeiss models.
When your investing in a tiny optical instrument, optical performance is of utmost importance, and having purchased a monocular five years ago, it goes without saying, you get what you pay for.
Regarding price, you have to spend a lot of money, to justify buying a monocular, as optical quality differs considerably from a decent one, to one that provides a superb image.
You are far better off getting a pair of decent quality compact binoculars, than spending a small amount of money on a budget monocular.
The image quality from a budget monocular will be poor, so poor in fact, that you will probably not want to use it.
I am saying that, from personal experience, having looked through over nine different models.
Due to their small size, and small magnification, unless the glass used in their construction is of the finest quality, the image will be poor, or at least blurred at the top end of the magnification.
After nearly a year, in comparing the various models, at all price points, i eventually picked up the courage, and blew £345 on a Leica Monovid, from Cleyspy, in East Anglia.
I know, £345 was a high price to pay, far too much for your average person, but the image quality is razor sharp, and like all Leica instruments, build quality is magnificent.
Due to its tiny size, of only six inches long, it travels with me on most of my walks, simply because its a joy to use and own.
Unless your prepared to spend a lot of money, for optical performance and precision, its far better to buy a 8x20 compact binocular, than buying a cheap monocular.
Unlike the small compact binocular market, where you can spend an affordable amount of money, and achieve great performance, its entirely the opposite when you look at monoculars.
To achieve an acceptable image quality, you unfortunately have to spend a lot, to achieve it.