I can’t see where you are based
I'm going to take a wild guess at the Czech Republic
Pytlak, good question.
Not sure you would see a big cost difference between providers because the kit comes from Robinson in USD $. Therefore it's worth computing the dollar to local currency of the provider conversion and then back to you in Euroland. The bigger leverage may come from Euro to another currency where you get a conversion rate in your favour. This may involve creating and shipping outside the EU.
At the moment the GBP favours exports because you get more £ for your € but will not affect the $ rate which is still the same. You may be better asking a banker .....
If you are looking for sites then in the UK, Aero Maintenance at Walton Wood due overhauls. So do Sloane, Heliair and HQ (google for contacts). There was a recent video on the Heliyorks Facebook page of a 44 being stripped for overhaul which may be of interest and give you another name.
Summary:
1. Dollar rate conversion to country of overhaul
2. Country to Czech (€) rate for labour
3. Labour rate of supplier and conversion to your cash in €
4. Cost of shipping v cost of flying to site