@alexxx
If you ever want to ride a trials bike in ‘competition’ in France get one with a carte gris and don’t whatever you do buy a trials bike in anywhere else but France! I live in SW France and brought over a Beta Evo, registered in the UK, and whilst it could be registered here, it was going to cost much more than selling it and getting a French bike.
Riding trials is so different to the UK, needing a road bike licence, insurance and a bike that is registered for the road. Amicale trials are getting popular, which don’t require the bikes to be registered etc., but they aren’t everywhere yet.
If you’re just messing in the woods however, then buying something without a CG should mean it’s cheaper and you could use it to force the price down.
As for which bike, go on the condition rather than the make. At your price level it’s more important what might need to be spent on a bike. Refurbing a trials bike can be very expensive, so take real care and don’t buy one that needs work unless it’s very cheap.