Potting soil is unnecessary for raised beds - more or less overkill :-) Because raised beds have an open, freely draining base, all you need is a good, loose, fertile soil.
Look for a quality 3- or 5-way planting mix, sometimes called garden planting mix (I believe PT refers to it as "special planting mix"). These all have a compost component and are ideal for most types of planting situations.

For this type of activity - filing raised beds - you always want to look at bulk soil services rather than purchasing bagged goods. Unless you are dealing with one tiny bed :-) For example, 1 cubic yard of PT's special mix retails for $26.75 picked up. The equivalent volume of a similar bagged product even at bargain rates would run around $100.00!!

And yes, they do deliver but the price per yard is higher and there are minimum loads. Often it is best to borrow a pick-up and drive out and get what you need yourself. They will load it for you.....you just get to unload it once home :-)

Good advice, above.

And yes, you can plant in just compost; there are folks here who dump a foot of dark compost on their lawn and plant vegetables every year, and then replenish the compost to the foot depth the next year. No boards or anything.

But the soil mixes will hold their volume better. No need to fill your kits more than 18" deep. That would be fine for fruiting shrubs. Vegetables take even less. Pack the soil every few inches while filling else plan on some settling.

It is quite possible to go overboard with the organic matter and nutrients.Too much of either becomes limiting. You want your raised beds to be mostly soil, same as when planting in the ground, and not soil-less potting medium. Potting soils are developed to make up for the lack of air movement through container walls.

I've successfully grown in nothing but Cedar Grove compost with the addition of a small amount of sand and compost generated from my yard.

Compost is considered a soil amendment. It is not intended to be a sole planting medium although it can certainly be used to supplement any type of garden or potting soil. But not take the place of :-)

Compost is only partially (OK, mostly) decomposed organic matter. It contains none of the mineral components of a true soil so may very well be lacking in certain micronutrients. And because it is only partially decomposed, it will continue to break down over time, compressing and collapsing and becoming waterlogged and impeding good drainage.And because it continues to decompose, it shrinks. You can expect a 25-60% reduction in volume of compost over the course of a full growing season, depending on how "finished" it is to start with.

One can encounter all manner of anecodotal experiences about growing plants in less than ideal media - heck, hydroponics grows plants in nothing but water - but it is not always the most efficient or productive method. There is a solidly scientific reason why potting mixes and garden blends were created!

the trick is where to find a good non contaminated mineral soil that is not full of weeds or chemicals.

After all these years, I still find compacted construction debris hardpan a few inches down when I go to plant something in a new place.

Dump good soil on top, plant in that.