OP I work in the industry and can give you some advice.
The price per sqm will vary according to the thickness and type of insulation you want/require and also the finish that you wish to put on top. Dry dash render, coloured render, brick effect etc.
Expanded polystyrene (EPS) is the cheapest insulation but you need to use a reasonable thickness to achieve a decent level of performance, usually at least 100mm.
Something like Kingspan K5 phenolic insulation will give a similar performance for roughly half the thickness of board, but this is more expensive.
Its important to consider openings, fixings, gas supply and roof overhang etc.
As someone mentioned Wetherby Building systems are one of the main system providers. It might be useful speaking to SPS envirowall as they have an outlet in Wales I believe.