An alternative within your budget could be E63 AMG, but only the one with the proper AMG 6.2L V8.
As big V8s go, they are impressive, 500bhp, 7500 rpm and no superchargers or turbos to worry about. XFR's very nice too, the supercharged 5Litre is tuned for low end torque, but I'd be worried about reliability, especially transmission and electrics.
As nice as the C63, E63, ML63 etc.. With the M156 6.2 V8 N/A engines are they have been known to have their own problems. Not very common, Granted. But would always be at the back of my mind... I believe most but not all of the niggles where fixed from around 2012/2013>... Earlier cars from 2006-2012 that had the M156 6.2 V8 N/A engine fitted could have issues such as the head bolts snapping, lifter issues, cam shafts... etc..
No idea what the newer E63 with the 5.5 V8 Turbo are like for reliability. Maybe they would be the safer bet?
Only powerful Mercedes I’d consider would be one fitted with the what’s considered a pretty reliable engine. The M113 5.4 V8 N/A or M113K 5.4 V8 Supercharged... Although I believe these ended around 2006 for the E55 / CLS55.
Take these for example, Very nice car’s IMO.
https://www.autotrader.co.uk/classified/advert/201903226155313?atmobcid=soc4 https://www.autotrader.co.uk/classified/advert/201903196043905?atmobcid=soc4