It depends on what you want. I'm personally not a big fan of gravel or rock, as it tends to make things difficult in the future if you or someone else wants to remove it. A possible alternative would be to put down a weed control fabric and cover with woodchips. Woodchips are inexpensive, and sometimes free. Where I live, we can get free woodchips from the electric company. I'd suggest working on a plan to potentially include in some plants that are native to your area to help the pollinators and other wildlife in your area. Allow the plants to fill in nice and thick and they'll out-compete most weeds, especially after the first year or two. I'd recommend looking for native seed mixes, which would be the cheapest way of doing it, but keep in mind that you'll likely have to wait to spread the seeds in early winter because many seeds need to sit through a winter before they'll grow. Otherwise you could buy plants, but the cost would be more than buying a seed mix.
Here's an example of what you could do:
I have a North American native garden and I thoroughly enjoy it. This particular area in the photo below was the first to fill in, and when it did, maintenance became minimal. No watering, no fertilizing, no special care at all. Occasionally, a weed or two starts growing and I pull them. It does take a couple years for the plants to out-compete the weeds, but once they do it becomes significantly easier.
Meanwhile, surrounding my pond, I use the woodchips and weed control fabric method, and it really makes things easy. The occasional weed pops and and I pull it. I don't think I pull any more than 30 weeds a year, and usually it's right where the weed fabric stops.