I actually went out and bought the dirt. We have a dirt supply place nearby, and it's foolishly cheap. This took one (Toyota) pickup load, and I shared the load with two of the other beds. Two truck loads cost what a couple of starts would have. (But I had to shovel it all! That's a lot of work!)
The "dirt" they sold me is ⅓ topsoil and ⅔ mushroom compost. Mushroom compost is the best stuff in the world. If you're gardening in that, you need to stand behind a tree and just throw the seed at the soil, so it doesn't hit you in the face when it sprouts! That's why they "thin it" with topsoil! It's for your safety!
Our excuse for the new bed was that we want to try growing sweet potatoes this year. Yeah, I know they aren't supposed to grow here. I grew some amazing cantaloupes and watermelons last year. Don't tell me stuff won't grow here: that means I have to try it!
Now I gotta find a home for that stack of sod I pulled up for this. . .