Tough to say. But I'd still scale him below the base Saiyans. It depends on what multiplier you believe is more viable to the SSJ at that point. Since I'm generally using a 50x one, I'd give him a 5,000,000 battle power or so.
If going with a 10x, he could be as high as 50,000,000 imo. It's also worth noting that Goku insisted to Chi-Chi that he'd be important in the upcoming battle, so maybe having him this strong with a lessened SSJ multiplier can make more sense.