Whiteline makes an rear anti roll bar that is popular in the European Astra community. I think the model BHR75Z fits the Saturn Astra too.

A few are for sale on ebay for $99 (free shipping). The list price is $357 but I don't know what the typical market prices are.

US website
https://whitelineperformance.com/us/...86-bhr75z.html

Fitment guide is downloadable at the UK site
https://whitelineperformance.com/uk/...86-bhr75z.html

Generic fitment guide
https://www.astraownersnetwork.co.uk...607/?id=118607

I think Whiteline is based out of Ontario (California).

 

As always, thank you for sharing