I am shipping 12-15 boxes across the country, what is the cheapest way to do this?

I’m moving on the 1st and need to ship my entire life to California. I did this a few years ago (moved to Florida) but I can’t remember exactly how I scheduled to have the boxes picked up and shipped so that I would receive them on a certain date. I know sites like FedEx have a way for you to enter the size and weight of the box and I will definitely look further into that but I am wondering if there is a cheaper way?

I would like to boxes to arrive by the 3rd of December, and I plan to have about 12— 15 boxes (ranging from book sized to extra large) all under 70lbs.

Does anyone have any experience doing this or something similar? Would it be cheaper to look into moving companies? How do I go about this? I’m so stressed out over this stupid stuff, I need all the help in the world – and you guys are by far the best :)