What should customer acquisition cost be?

At most what a customer earns you over the whole time they buy from you - and healthy is no more than a third of it. If one customer brings $900 of lifetime margin, you can spend around $300 to win them and still have room to profit and grow.

Calculate it as total marketing spend divided by new customers in the same period. What matters most is whether you're counting a single purchase or the whole relationship: with repeat purchases you can pay more than the first order returns, with one-off purchases the first order has to stand on its own.