There are 2 main types of spray foam used in ireland, open cell and closed cell. Open cell spray foam is used primarily in office or residential applications. Closed cell spray foam insulation is used in commercial and industrial applications or on containers, farm sheds etc. So the use of the foam will determine the cost.
The economies of scale apply when figuring out the cost of spray foam insulation. The larger the area the lower unit cost per sq foot or meter.
The more layers of foam applied the more foam required.
If you are insulating a farm shed, will scaffolding or a cherry picker be required? If it is this will add to the costs of spraying the shed.
Spray foam is famously quick to apply so labour costs are generally less that for other insulation materials.
As a rule of thumb the cost of spray foam insulation per sq foot or per sq meter is often not the best question to ask. Rather ask how much does it cost to insulate my shed or attic? Then give a square foot or square meter area and tell the contractor the depth required and the ease of access.