Acquisition costs increasing while AOV stays the same

I've noticed I'm gradually spending more to acquire each customer while the amount they're spending per order has barely changed. It's not killing profitability yet, but if acquisition keeps getting more expensive I can see it becoming a problem pretty quickly. I don't want increasing ad spend to be the only answer either. How are you dealing with this? What have you focused on when acquisition costs started growing faster than the value of each order?