Well below your budget but I picked up a refurbished Sonos Beam Gen 1 direct from Sonos for £269. Came in original box with cables and condition of unit was basically brand new.
I've just been using TV speakers for years and as it was my first foray into a soundbar, so I didn't want to spend too much money in case I didn't like it.
Wow.
Makes a big difference for TV and I was watching a Marvel film last night on Disney+ and it sounded epic.
It now also doubles up as my Radio and HiFi as it can stream BBC Sounds and Youtube Music/Spotify, all voice controlled via Google Assistant. I'm even tempted to pick up a couple of Sonos One speakers and have a true 5.1 set up now.
I'm not an audiophile and there might be better brands out there, but I'd recommend anything from Sonos based on my recent purchase (Beam Gen 2 is within budget at £425).