I don't buy FB traffic currently. But logic about machine learning says it needs data. If you can't justify getting enough sales due to the price point, then facts are facts, you need more data, if your conversion pixel is on the thank you page, it cannot collect data, so you need the next best conversion point that also generates enough data, but the conversion point has to be as valuable to retarget as say the conversion sale point: ie, checkout page abandons, cart abandons as your point for a conversion pixel, as far as I am aware you have different options to tracking as far as conversion pixel is concerned, not only just sales, unless you just want clicks, I wouldn't use web traffic because you'll teach facebook you want to see a bunch of entertained people that can't afford your good but like to look at it. Stick with conversion objective but make sure your tracking it for the next best performing data conversion point that also generates enough data; since your can't justify enough sales to teach the machine learning model with a $3000 product.