Buy a Nikon or Canon crop sensor camera. This way the focal length of your lens will be multiplied by 1.5 for the Nikon, and 1.6 for the Canon.
Don't buy a full frame camera, unless it's as your second Camera- useful for static shots though.....
With the crop bodies (Nikon D200, D300, D500, D3100, 3300, D5300 etc), a 200mm lens is a "300mm" on the Nikon and a little longer on the Canon.
Buy a good lens. I think the Sigma 50-500 OS is the best tele for air shows.
Second hand maybe £500?
If you can afford it, get a Nikon D500 body.
There's some good advice!
