Do you have a bike already? If so, a set of rollers, preferably ones with resistance, is a great thing to do in winter if you can't get outside. I use mine in winter, sometimes even when I could get out, just because the roads are always wet and I don't want to bother getting dressed, washing clothes, and cleaning the bike afterwards. Even an very nice set of rollers:
https://www.sportcrafters.com/produc...ve-pro-rollers
are still less expensive than a good bike.

Of course if you don't own a bike, a spin bike will work fine for your purpose.