Which air rifle

I suggest you go into a store and try some. Different models will be different sizes and depending on your stature and needs this may be important. A 110cm rifle is good for portability but if you want something more powerful this will typically be 120cm.

PCP will not be an option anyway. I am assuming by your post you do not have an FAL?

I recommend gas over spring.

A powerful rifle like a Gamo Swarm (or any of their Mach 1 models) offers great performance rivaling PCP but take more effort to cock.

At 40-50 yards a 3-9x40 AO optic is a good choice. Any further and you will likely want to get something better.

Also allow in your budget other necessary items - a pair of ear muffs if you don't have them. I suggest level 4 max because level 5 are a bit fat. And a gun bag because you will want to take it places and you need to keep it packed in transit. Some gun stores even require it packed when you bring it in.