The Opticron DBA VHD+ monoculars retail in the region of £300.
But, my reason for purchasing was to experience a type of optic I've not owned/used before, because I only have one eye in working order (just for the time being, hopefully!). I'm simply using my temporary disability as an opportunity.
Make no mistake, I would not recommend a monocular as an alternative to a binocular. A monocular is a compromise. Apart from being half the size and weight of an equivalent binocular, making it lighter and more portable, the view is not as relaxed or enjoyable as the view through an equivalent binocular (there's a reason why monoculars are not so abundant on the market, they're a compromise and quite niche).
And, take my experience of the three monoculars I've tried and tested with a pinch of salt. The one I'm keeping is the only one of the three which fitted me straight out of the box. The other two didn't, although with a little time (and o-rings) the 8x42 DBA VHD+ would have been just as comfortable and as much of a joy to use as the 10x42, for sure. The problem was me, not the monocular. The experiences of others with the same three monoculars will be individual to them, and inevitably different to my own, unless by coincidence.
There are other monoculars out there, different designs and with different types/location of focus wheel. I auditioned just three, based purely on my uneducated perception of what I was looking for, what I thought I might prefer, and recommendations from other forum members.
The most important rule to follow (if you can) when purchasing optics, is try before you buy, spend as much time as you can testing the instrument in as diverse conditions/situations as possible, and compare them side by side with other brands/models. Use spec sheets and opinions of others as a guide, but make the final decision based on your own hands on experience.
James