Would buying a bike stand better than getting a dedicated stationary bike?

A stationary bike can not be used to get anywhere.

The most obvious question for me would be how difficult would it be to change it from road-ready to stationary. Perhaps the people you would buy the conversion kit from could tell you about that.

You mean using a regular bike on a stand for indoor cardio exercise?
Well, I’m foreseeing one complication. If your back wheel is spinning freely in the air, you won’t have a lot of resistance to work against, which I think is kinda the point of exercise, isn’t it?
Or maybe I’m visualising this wrong.

he could put the backwheel in a tub of thick syrup.

The only thing that occurs to me is that if you like the “spinning” style of stationary bikes, it would seem to be an advantage to set up the conversion kit on a road bike and so come up with a similar setup to a spinning bike, because stationary spinning bikes are way more expensive than regular stationary bikes.