Cheapest? Probably look for a 2nd hand Yamaha RX-V583 or V585. Update either to the latest firmware which adds eARC. I've seen the V583 recently going for less than £250 through now due to seeming shortages of many AVR's then approx £300 maybe more typical.
You'll pay near £500 for the Sony 1080 which is holding its price amazingly well due to the fact it is still the 'current' model.
@Raymond Lin I would advise you to get a 9.2 receiver to future proof yourself if you ever wanted to try Atmos 5.1.4.
I would compare Atmos (for your hearing) to OLED (for your vision) in that once you tried it's hard to go back.