Kettlebells are a fad and probably about the poorest weight you can use for strength training. Dumbbells are much more versatile. Try doing incline presses or french curls with kettlebells, for example.
I don't know for sure, but I think kettlebells became popular because of the "Biggests Loser" TV program. However, the reason is not important. They do have a place in a full facility gym but for a limited home gym you'll find they limit you much more than dumbbells.
We can't tell you what weight you should begin with because we don't know anything about your training goals or your physiology. But if you think kettlebells look like fun then you're going to love dumbbells which come two to a set. They offer the advantage of being able to push weight over head without it hanging. It's also much easier to do laterals and flys and similar exercises with dumbells because there are two which makes for a symmetrical workout rather than one weight which can pull you off balance. You grip the center of gravity in your hand with dumbbells but the kettlebell has a center of gravity below your grip which makes them more difficult to wield and forces them to rotate in your hand which can cause callousing. Etc. Kettlebells are an old fashioned training weight which was used long ago (circa 19th century, I think) and there are much better weight to use today. I personally have no use for kettlebells.
You might want to check Craigslist for weights and be sure to spend no more than $1 per pound.
Good luck and good health!!
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