If you are just beginning, buy any bike that fits you, ride it, and enjoy it. If cycling really is for you, you'll be buying a different bike very soon no matter what you choose the first time.

Just make sure it fits you and if you aren't confident about how to judge this, buy from a bike shop, rather than used.

There are very few of us here who ride regularly and who are still primarily riding that first bike.

Also, there are very few of us here who did not change our idea of "affordable" vs. "too expensive" in our first 0-2 years of riding.

Enjoy. You may just be embarking on one of the great adventures of your life.