For a US tax resident, what’s the cheapest way to hold Euros domestically (without triggering FBAR)?
Interactive Brokers is free, and the exchange prices are as close to wholesale as you can get.
various of the currency trading platforms will also let you “hold” EUR. OANDA is one of the oldest and IMO reliable ones.
One might ask why you want to hold EUR domestic. There are a number of different reasons to want to do this, and simply holding EUR may not be the best answer for any number of those reasons.