I've used two-part spray foam kits in houses on very uneven surfaces. On the nice flat surfaces of my new shell I decided to use Celotex and I think the result is better. If you're only doing a section at a time you might need to use smaller kits which work out more expensive. I'm not sure how long the resin last in the hoses and gun once they've been attached to the bottles. If you use half a kit then try to use it again a few weeks later it might not work; but you get plenty of nozzles so it might be worth a try. In my experience, the coverage quoted is difficult (not impossible) to achieve in real life so factor that into your pricing. Doing some quick (hopefully correct) calculations, 50mm Celotex works out about £150/m³ and larger spray foam kits over £400/m³ , using the manufacturer's figures. You need to add the cost of aerosol spray foam to the Celotex but that's quite a difference.