Hi Dave, I’ve never actually reviewed one... might be worth a question to Andy’s Airgun Review Group on Facebook, the community there are normally full of help and advice. Kind regards, Andy.
I don’t think any decent thermal scopes are ‘budget’. I‘m luck to have access to a friend’s Pulsar XD75 and it is fantastic, but ~£3.5K when new! Image intensification like the Pard or the Sightmark Wraith at £500-600 might be a better place to start with?
If I had £5K spare (!!!!!), then this would be on the shortlist: