Pick from here, Millsy. There’s a wide range, the one for £800 in there new. If you’re looking at a decent second-hand one, the expensive ones here will be a good kind in terms of brand and type.
https://www.bikeradar.com/advice/buyers-guides/best-gravel-bikes/
I’ve refused to get one, but so many of my mates have now got one, I’m gonna be an outlier at some point over the summer.