If you are looking for high quality and affordable sights to use for airsoft, just look at RedWolf Airsoft and RWA for the GK Tactical optics. You can choose from the 552-style holosight to Aimpoint-style replicas and they can easily meet your budget. Just go to RedWolf Airsoft UK to check them out.
Available at RedWolf Airsoft right now is the affordable Red Dot Sight from GK Tactical... "GK Tactical Adjustable Red Dot Sight fits on a low profile mount, suitable for standard 20mm rail mounts. This small reflex sight is perfect for those of you looking to go minimalistic with accessories, featuring the sensor that means once you have inserted the battery, you are all set to aim and terminate your targets.
This time the Red Army Airsoft Club reviews an airsoft gun not made in Russia, picking up the GK Tactical Glock 18C Gas Blowback Pistol for this video. Made in Taiwan, this pistol has a metal slide, outer barrel, and magazine. It also has an adjustable hop-up and the of course, the rail frame design for mounting a flashlight or laser sight.
Affordable adjustable red dot sight from GK Tactical available at RedWolf Airsoft for US$47.00. This can readily fit airsoft guns equipped with 20mm rail mounts... "GK Tactical Adjustable Red Dot Sight fits on a low profile mount, suitable for standard 20mm rail mounts.