That unfortunately would be a hard one to answer at the moment ,especially with people watching their cash,however could be alot downgrading from lorries atm,depending on the condition i would maybe say 2.5-3k(but obviously that depends on the usage and as said above condition??without pics hard too say)
The batesons are more new than a ifor you can get a 505 for less than £3000 new with some hagling, a bateson ascot about £4000 but remember there bigger and better quality than a ifor....
I've got a cheval liberte and they kind of look similar to the bateson? I know they are lightweight like Batesons compared to the traditional trailer and I bought mine off of ebay for 2,500. I think aim high and then you can always come down a bit . Good luck