Pesto is mainly expensive due to the pine nuts. Pine nuts are sometimes eye-watering costly, and quite a bit is required to make a decent amount of sauce. The cheapest pesto I have found is at Costco. The only problem I find with that, as with everything in Costco is that I have to buy a huge tub! So I only buy it if I’m feeding a large crowd, but it sure is affordable! And the taste is not bad too.