I suggest you contact Kingspan and ask them for a list of who installs their external insulation board (K5). Contact these and get them around to survey your job. It may be straightforward or there may be many issues such as insufficient overhang of the roof, drain/down pipe problems, awkard windows, scaffolding required etc. All which I guess can be overcome by the installer.
Prices seem to vary from about 100 to 150 euro per square metre. So a quick run around with a measuring tape will give you a idea what to expect.
Regards
Franm