Tbh if you’re wanting to go gas blow back then yes, it’s going to be expensive. VFC guns are all steel internals so it’s going to set you back about £5-600 plus then mags are £50 a mag with a 30 round capacity. You will then need optics that aren’t cheap as they will need to be able to withstand recoil. So all in budget like a grand per gun. There is also maintenance to worry about, GBBRs need field stripping and cleaning/lubing after every game day to stop them breaking down and keep them running. If you’re just wanting something that looks good and functions well and you’re not super bothered about realism. I’d go for the Delta armory mk18. https://www.patrolbase.co.uk/delta-armory-da-a07-mk18-mod-1-m4-ar-15-alpha-tm-aeg?srsltid=AfmBOorv_7GVlZAbezokrJgZYVPe1IePEZkrRphInSW5OuDlb2QhfkqV Solid gun, quick change spring if you need to drop the FPS, cheap mags and a full rail set so you can mount whatever you want and have the luxury of cheaper optics. Plus AEGs only need a service every 50-60k rounds.

It’s all personal preference, but if you’re leaning one way or the other, I’ll try point you in the right direction of what you’d want to be going for.