In my PCP stable at the moment, all £500 and under.
Weihrauch HW100
Weihrauch HW100K
AirArms S200
AirArms S310
Airarms S410
To be fair, there isn't much between them in accuracy. When I say much, the HW's have the edge, but its down to the width of a .177 pellet @45 mts. But then again this could be down to the pellet brand that suits the gun. So I'll make a sweeping statement and say they are all as good as each other. Bench rested, all of these put a pellet inside a pound coin @45mts
You'll struggle to get a decent HW100 for less than 500 quid. The AirArms can all be got for £300-450
The AirArms are simple to take apart and service yourself. The HW's are a far more complicated animal.
If 600 quid is your total budget, all of the above should be within range with something like an MTC 3-12x44 Viper