there are thousands of places.
some even give you a .com for free if you get hosting from them!!
Be careful with this arrangement. You are not given administrative or technical control in this type of arrangement. You host has all of this. What happens if later in the future you want to move hosts and you can't transfer the domain?
Be willing to spend to secure your domain so you can maintain some level of control over where it exists over time.
You can get domain name almost everywhere but to find the cheapest one is by using coupon code. For a bulk purchase, I always recommend Godaddy since there are lots of coupon codes shared on the internet everyday.