It's still a big difference, but it gives you a starting point. Compared to a standard 4-inch deep concrete slab, a 6-inch deep slab provides more structural support and better crack resistance. There is also a crack-resistant concrete, which has a synthetic fiber mixed to help prevent cracking; it also does not require steel reinforcement in the supported slabs. Four to eight inch thick concrete slabs are mainly used for driveways, patios, sidewalks, and garage floors.
On a good compacted gravel foundation, a 4-inch thick concrete slab will be all you need to build or place a pre-built shed. For heavier loads, such as trucks or more than an average vehicle, you may want to ensure that your concrete slab is no less than 20 cm or 8 inches thick, as increasing its thickness will increase its carrying capacity, not just its price. Unless you know the dimensions of the area to be filled with concrete slab, it can be difficult to get a cost estimate. Wet concrete is also considered toxic and can cause chemical burns, so take appropriate safety precautions to make sure you don't expose your skin and eyes.
It also prevents problems such as water buildup under concrete and reduces the likelihood of erosion and sedimentation. If it looks like the concrete mixer will need to use a concrete pump to pour the concrete, it will probably be at the upper end of the scale. A 2-inch thick concrete platform in Florida won't survive the winter freeze-thaw in Idaho or New York. However, the thickness must be increased if a slab is poured onto soft clay or if it is required for larger buildings.
Any error during the preparation, pouring, or finishing phases can result in premature cracking, improper drainage, or an undesirable finish. Your final cost will depend on the size of the slabs, the thickness, and if you have any special reinforcement, such as wire mesh or reinforcing bar. This mixture is poured onto a gravel bed bordered by a wooden frame, the latter typically made of standard wood such as 2x4s or 2x6s. The process is time and labor intensive, so set aside at least a week to complete it, which should cover everything from preparing the mold to allowing the concrete to set and cure.
If you're comfortable measuring the project, then you can get a rough cost estimate without calling a professional.