There is no reason to install a concrete slab as a base first. So lets say that costs $8K. Then you lay a $8K paver installation over it. Why do the concrete when paver installations are designed with $500 gravel bases, and they work and perform just perfectly? All you are doing is expanding the contractor's scope and money in his pocket. The only thing I can think of where you might consider that is with expanding clay in TX.

Here is the order of finishes, both in looks and cost respectively, starting at the bottom:

concrete < stamped concrete < pavers < natural stone < gold bars

There are variations and higher end finishes of each specific one, but that is the basic general essence. Note that you don't combine them, so no concrete under pavers, no gold bars over stamped concrete. I would suggest looking up Unilock or Belgard, the two behemoths of the interlocking paver industry, their websites have some good pictures and descriptions of installation methods.

That's really not accurate^^^. You can install on concrete, but there's a difference between all fresh vs topping an existing slab for a typical patio.

Concrete runs $120-$200 per yard, CA-6 $50. A concrete company will charge from $5-$10 per SF for a slab. Could you get away with just a rough screed instead of bull floating it to perfection? Maybe, but you'll probably have low spots and ridges from aggregrate collecting water. And concrete is not designed to move, gravel bases can. Concrete is not designed to drain water (which is why it is recommended to drill holes), gravel is. If that slab heaves for some reason, there's no fixing it. If a gravel base heaves, remove the pavers, repair base, and reinstall. Compaction of a 4"-6" base is just that, there are no lifts. Concrete laborers are much more expensive than landscapers, not even talking about concrete finishers.

If you like the look of concrete or stamped concrete, do that per industry standards (gravel base as needed for poor soils). If you like the look of pavers/porcelain tile, do that per industry standards (gravel base). If you like stone, do that per industry standards (gravel base). Now, if you live in a non-freezing climate and want brick or stone with mortar joints, then you can start with a concrete slab.

I mean, I've priced it both ways and job costed after the fact and found the #s pretty darn close but ¯\_(ツ)_/¯

There are some situations where concrete makes more sense. A new house where we're going right up to the foundation wall, no homeowner is spending what it costs to excavate all the soil to undisturbed (basement footer) and come all the way up w/ gravel in lifts compacted to 95% proctor density. But we can use sonotubes and dig a handful of piers and tie the slab in pretty cost effectively.

did learn something interesting....the pavers are warrantied by the concrete is not. if concrete cracks we are out of luck. I am in NE OHIO and a local contractor said concrete base is the best and a very reputable landscape design firm said gravel and sand. The landscape design firm said there is no guarantee on concrete not cracking with time. If, by chance, a paver cracks...it is easy to replace.

we are going with the gravel/sand base....lots of roots in area and I don't need cracked concrete (over time).....thank you everyone for your suggestions and input.