I'm on my original GD3 battery so have been looking for a replacement. I'm also a NAPA customer on their mailing list, and they're having a sale right now. 151R battery - $82.80 down from $91.99:

NAPA AUTO PARTS

But if you use their $10 off coupon from the last mailing list - plus their $2.99 NAPA bucket which allows another 10% off - the final price for me was $74.08 with tax. Free hat, too. That's as cheap as I can find a new 151R battery anywhere. Typical price is over $100.

I already had a core trade-in off a Ryobi 48V lawn mower, which they accepted toward the car battery. I kept the old Yuasa battery from the GD3 and will keep it charged for emergencies.