Ten to fifteen cores, four to eight inches, one bag
How ISU Extension describes a home soil sample, and when to take it.
A useful sample is 10 to 15 cores taken across the area you care about, mixed into one bag. One core from one spot describes that spot. Depth is 4 to 8 inches, with mulch, roots, and manure kept out of the bag. A quart freezer-weight bag is enough. County offices hand out kits; the form can also be printed and the soil sent in a bag you already own.
Fall or early spring is the window, any time the ground is not frozen. Sampling at the same point in the year is what makes the next report comparable with this one. Home ground is on a 3-to-5-year rhythm unless something is visibly wrong sooner. Turnaround, once a lab has the sample, is described as a week or two.
None of those figures is a price. If you need a cost, read the lab's current form. This page will stay blank on that line rather than estimate it.