Facebook marketplace, they often don't get much use! But I didn't get one until I needed it after the baby was born! It's definitely not a necessity
I have the bugaboo one - expensive but it has a bassinet feature which is useful for when baby is tiny and can't sit up yet
We have a Joie one, from Argos, which has the option of a bassinet top and is really handy / easy to use. I think it was around £70 x