50€ for 100ml is quite cheap actually
I paid £38 for 100ml here and I have heard of others paying £50-60 normally, I'm lucky in that my poultry vet only deals with poultry and normally on a farm scale so they tend to be cheaper for drugs etc. The thing to remember with 10% is that it has a fairly long shelf life until you open it - it is meant to be used within 30 days of opening. Personally I don't think respite, acv etc are much good for respiratory problems.
The oregano based products do help but only really as preventatives so you need to use them permanently or perhaps 1 week on, 1 week off. Ropadiar (which I use), Orego-stim and Herban are fairly widely available now.