TBH, the thicknesses you're going to be applying this stuff with, it won't make a jot of difference overall.. it's not like it's going to be sprayed on the underside of a roof as the thermal envelope of the house. A 5mm fillet of it gluing a sheet of celotex between your rafters isn't going to double your heating bills if you use the ever build vs the soudal. I doubt you'll beat .03 for this foam (it's PUR but not the same structure as kingspan etc and not made in the same controlled conditions)
One thing to note, these lambdas will have been measured in lab conditions on perfectly expanded foam, if it was even tested rather than assumed. You won't get that on a cold site, from a knackered gun and an over enthusiastic application between two nonporous surfaces (for example)
In terms of cost, cheapest source of soudal for me has been a seller called platinum-supplies on ebay.. about 3 quid a can if you buy lots (they have a listing for 12 where the post is separate, so you can get multi boxes of 12 for reduced postage), and that's inc vat. You might be able to contact them direct and get a few percent more knocked off if they don't have to pay ebay and PayPal fees. eBay for "soudal foam 12". I note now that someone else is doing a box of 12 a couple of quid cheaper. If you're newbuilding and making a vat reclaim, be sure to check the eBay co you buy from is vat reg.. sometimes eBay sellers look cheaper until you realise they aren't vat reg and the more expensive guy will be cheaper post rclaim
