Either would work. If you already have a monitor that's satisfactory, a cheap pair of speakers would probably be the most practical. There are tons available from your local electronics store or web stores such as Amazon. And if you have a store in your area, you might be able to find a used set, or perhaps from time to time in places like Goodwill. You would want speakers that have a 3.5mm stereo plug or that can connect via USB; you'd want to confirm compatibility with Macs for any USB speakers, though most should work. You can also use Bluetooth but that may be more than you need unless you want the speaker(s) to be portable.
Regards.