Before you make your purchase, consider how much you plan to use the monopod, the weight of the lens/camera combo(s) you'll be using, the weight of the monopod itself and the features you deem most useful. I shoot birds with a Z9, Z8 and gripped D850 and long lenses (including a 500 f/4 and 800 PF). The 500 f/4 with a TC and adapter can weigh 7 to 8 lbs or more. I typically handhold, but when I've needed support I've turned to my Gitzo Series 3 systematic for over 12 years. It's been great, and I've always felt good about the purchase. In fact I have two Gitzo tripods, the second being a smaller, lighter, used model for macro photography. However, while never having owned a monopod, I decided last summer that I wanted to have some support without the weight and bulk of a tripod. So, in my early 70s, I decided to purchase a monopod.
I first looked at Gitzo, but after seeing the price, I decided to also consider other well-known reputable, but less expensive, brands such as Sirui, Vanguard, Benro and Induro. I eventually settled on the Benro MSD46C SupaDupa (mentioned above by froolk) for $160 and the Wimberley MH-100 head for $170. The 6-section Benro monopod weighs 1.3 lbs, holds 88lbs and has a maximum working height of 72". A Gitzo GM4255L, by contrast, is currently $389 on sale ($489 retail). It features 5 sections, 72 lb weight capacity, max. working height of 75 inches and weighs 1.6 lbs. So the Gitzo, on sale, is $220 more than the Benro with a 3" height advantage and 5 sections instead of 6, but with a slightly less weight capacity and weighing 0.3 lbs more.
In my situation, I didn't expect to use a monopod a lot nor, at my age, for a long time. When looking at the cost/weight differences, I couldn't justify the added cost and higher weight of the Gitzo. However, were I younger and more active and anticipating using it a lot, I might have given the Gitzo or other high-end brands more consideration. I raise this not to dissuade you from purchasing a Gitzo, but just to suggest you don't limit yourself to a single brand or price level based on just name recognition. There are a lot of good options available at a range of costs, heights, weights and features.