A lens like the Rokinon (Samyang) 14mm f/2.8 is a great lens to get started with and is very affordable.
A lens like the Rokinon (Samyang) 14mm f/2.8 is a great lens to get started with and is very affordable. If you're ready to spend a little more, the Sigma f/1.4 14mm ART or the Sony FE 14mm f/1.8 GM lens would both be great options. The best lenses for astrophotography often require significant additional investment, but in the meantime, the kit lens that came with your camera is perfectly adequate to practice the right techniques on. All you need to do is make sure you operate at the maximum available aperture size (typically around f/4 on stock kit lenses).