I reckon these "free" US brokerage accounts probably get you on the fx rates

I'll put a vote in for CMC.

I opened an account for my recently turned 18 year old son and the free trades under $1000 per day is perfect for the relatively small amounts he is putting into the market.

Set up was completely online and took about 1-2 days for the account to become functional.

I agree with @Shapeshifter I think we can put too much emphasis on brokerage costs rather than focusing on 'dial moving' matters. Here is a copy and paste from a post I did about 6 months ago on this topic.

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I use CMC and don’t trade enough (i.e. I buy every 8-10 weeks, I hardly ever sell, via a dollar cost averaging approach) to worry about the brokerage per se. That said, I always ensure I don’t pay more than 1% in brokerage and to put that into context, if I was going to have a $1M portfolio, this would mean I end up with “only” $990,000 (i.e. $1M less 1%).

I guess I ultimately lean to the view that there are so many other factors that will impact my total returns, and a (maximum) 1% brokerage charge is not going to make any material difference. For example, 0.5% brokerage means my theoretical balance above would increase to $995,000 – not a difference, in my view, worth worrying about.

If I was a day trader that may be different but then, you are probably gambling not investing but that is an entirely different topic for another day :)

CMC does charge a 0.6% FX fee on US share buy and sells. I've got a spreadsheet & linked word document where I put the buy/sell details in to calculate the costs and manually amend the details in Shareshight as brokerage (accountant was happy with this). I've been in touch with Sharesight to see if they could integrate this automatically (all the details are in the Trade Confirmation) but they put it in the too hard basket.