As others have suggested, the initial difference in cost of either weapon will soon become a non-factor. Once you own either one, you could shoot the 22 several thousand times or the larger gun a couple hundred times for the same cost of ammo.
Range time, targets, cleaning stuff etc, will cost the same either way.
The chance that you will get into a self defense scenario is one in a gazillion.
Add all that together and for me, it comes out like - Buy the 22 now. Practice and get good with it. Maybe get REALLY really good with it. Then, down the line, consider buying a bigger gun. You'll probably have a better idea about what you might want then. Maybe you'll have shot several more gun styles and calibers. If nothing else, you'll be very experienced at sight picture, trigger control, range ettiquitte etc.
You'll dig a quality 22, esp a revolver, the rest of your life.
Sgt Lumpy - n0eq