Ultra-portable, nice price, group 1 car seat?

[BlueHerring]

Would anyone be able to recommend a budget car seat which is very geared towards putting/taking in and out of different vehicles regularly? I suppose the key factors for this would be weight and ease of installation.
DS is 18 months old so Group 1 would be the target. It would be a "take to Grandma's" one to to complement the more permanent arrangement back home. Thanks!

[Boobybeau]

Not sure if it's budget but kiddy car seats are super easy and light to move between cars and have great safety ratings to

[Bamaluz]

Britax Prince is fairly lightweight and can usually be bought for about £60.