I would look at second-hand 'Gitzo 3 series Tripods' and a 'Lensmaster RH2' Gimbal for around that budget. - If you can push higher, then a Gitzo 5 series!
I used to have my Nikon D500/200-500 combo, on a Gitzo 3 series, which was fine..............however, once I upgraded to the 500 f4 prime, the 5 series was essential.
The 'Lensmaster RH2' gimbal, is incredible value for money at around £170.00 brand new, or second-hand for around £100.00.
Good luck with your search.