Aren't "market-sized" deals measured in millions because banks are making one deal to cover lots of smaller deals that they've made with their own customers?
If someone can cut out the middle-man and let the small deals trade with each other directly, there is no reason why people can't get the mid-market rate for a trade of $100 never-mind $1000.
This is the idea behind currencyfair.
And nobody (including you, Floyds or Jesus) can get mid-market rate for an immediate exchange of $1000:
1) The rate that you can get for a deal right now is different than the rate of the deal you made a minute ago - since the market is moving, but the mid-market rate is based on previous deals; so depending on rise/fall you might not get anyone to accept your deal at that price;
2) You can get market rates for market-sized deals, and that is measured in round millions; if you want to buy 1000 EUR, then that rightly deserves a markup of wholesale/retail;
3) In the common forex market, you don't get your funds immediately; spot deals are usually settled within 2 business days. If you want immediate money - then that is a different product with a different price.