What is the soil you have now like?
Why do you think you need to buy something called soil from a store?

If you're planting them in the ground, you don't need to amend with anything. Just put them in native soil and top with wood chips for mulch.

Here is a link that might be useful: Soil Amendments

Just as amending every planting hole may not be necessary stating that it is a myth that planting holes need amendments is also a myth. Those of us with sand for soil know that the planting hole does need amendments or it will not hold enough moisture or nutrients to support that plant, while some people with clay soils have seen the well amended planting hole become a bathtub full of water.
Since the 1960's most all of the soils I have looked at all over the USA have needed organic matter, but how to add that OM depends on whether the soil is sand, or clay, or loam. Even some clay soils do drain well enough that you could work lots of OM into the planting hole without creating problems but that also means you need to look at what you have.

kimmsr, a quick google search will show you what this product is - before you comment.

Irritated in Sugar Hill, GA, Rosie

roseview, I know what Soil Cycle is, a fairly expensive potting soil made mostly from compost.

The water mobility problem is one issue that can occur in clay soils, but another problem in other soils is that the roots may tend to remain in the amended soil too long where there is more nutrition and/or water holding capacity rather than spreading out in a normal growth pattern into the native soil. Amending a hole creates a 'pot' with different soil than the surrounding soil, no matter what kind of soil it is.

People still amend planting holes all the time anyway but if you're looking to save money, these shrubs can do just fine in native soil without amendments. Check around the neighborhood, if you see mature specimens of the same type of plant, then the native soil is probably just fine.

Maybe if you really feel like you should do something to get them off to a great start, consider inoculating your arborvitaes with micorrhizae, and use a root stimulant. These can significantly reduce transplanting stress. The micorrhizae develop a symbiotic relationship with the plant roots and help the plant to obtain water and nutrients from the soil. The root stimulant promotes root growth. If this interests you, do some online research for more info.

After planting, top with a little compost and keep the plants well mulched.

IMO if a tree or shrub can't be supported by the native soil, it's best to choose a plant that can. :)

Why do you think you need to buy something called soil from a store?

Convenient.

Lack of other options.

Needs something faster than building a compost pile now because all they need is OM for some point in the future.

Linda Chalker paper is misleading.
Soil amendments may work that way in clay or rocky heavy soils.
But in 42 years of working with plants, I have never seen this happen with sandy-loam soil.
We always worked up the whole bed, not just "a hole".
We work the amendments into the whole bed.
I am going to plant a Japanese garden: step one with be to disk & turn the whole area 12 inches deep.
This will kill any unwanted weeds & grasses & loosen the soil for the plants. All loose soil will be removed from the paths & put in the beds, to be replaced with gravel or stone.
In a garden with very large trees(oaks & pines) & Japanese maple,Dogwood,clyera japonica,are under story trees, perennials, bulbs. You are going to need more Organic material, just a hedgerow.

jolj, the Chalker article is not misleading at all. It states the reality for hole-by-hole planting. When preparing an entire planting bed for plant installation, the situation can be quite different. It's worth noting that even then, the benefits to the plants are likely to be minimal. We are much more likely to improve the local soil environment for our plants (in any kind of native soil) by the routine top dressings of compost and/or the addition of mulch.

I would recommend to phenixdragon that he/she use the money for some of those great Costco veggies. Mmmmmm, grilled asparagus....

No reason you can't do both. In starting a new bed we've sometimes been forced by limited amendment supply to amend only the holes. Then we mulch for several years with compost, shredded yard waste mulch, etc. which builds up the soil in the entire area.