Sub 10kg is going to be tough with most race seats since just the seat is typically 10kg. We're getting some of the Sabelt X-pads for our race car, they are ~7.5kg so side mounts, slider and adapter should be close to your target. The other option is carbon but they aren't cheap!
The Sabelt Titan standard is 9.5kg and $824, the Titan Carbon is 7.1kg and $2790..
I run Sparco QRT-Rs in my Cayman and they are ~7.5kg and sub $1000 seats. We're a Sabelt dealer and I really like their quality so that's generally what we suggest and use in our builds. Let me know if I can put together some pricing for you.