Quick update, as finally just purchased four new tyres.
After all the recos, thanks to everyone on SF, I managed to get costs from the online companies plus some local tyre companies. I wanted to go with a local company so openly told them what the online costs were. None of the local companies were able to match the online tyre supply cost, which isn’t particularly surprising, so what I’ve ended up doing is purchasing the tyres from Allopneus who were the lowest cost, then getting them installed at a local garage, who will also carry out a complete wheel alignment on the car. Allopneus do also offer the service of installing the tyres, which I did when I ordered tyres for the quad, but this time round I actually visited my local garage in the next village (who are also on the Allopneus installers list) and managed to even get a reduced installation cost when I combined it with wheel alignment.
So overall, I saved just over 300€, if I compare the total local garage cost versus the combination of online tyre supply and local garage install and wheel alignment cost - rather pleased 