StudioRSR in SoCal is another great option for a bolt in rollbar for E9X M3s. I'm very happy with the quality and fitment of their custom rollbars. They provide multiple options for each application and offer many shades of durable powdercoat to suit your needs.
It's a 2-piece bar that mounts to the factory top belt mounting points, then 4 holes need to be drilled into the floor to finish off the installation. Installation can be completed in 2 hours or less. Mention my name to Robert the owner, and I'm sure he'll work with you on the price a bit.
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