I'm not too up to date on this because I live where banking isn't an issue, but do know a bit. Many books do account transfers with each other.
Bookmaker and 5Dimes trade with the most sites.
Bookmaker.eu last I knew they charged $100 per transfer and $5,000 is the max. So if you do $800 it is still $100 cost, if you do $7500 it is two transfer ($5000 +$2500 and cost $200).
They have a thread here, maybe they'll answer the list of books they transfer with but not sure. When getting a transfer I don't think there's any charge but do have to rollover twice before cashing out (I think twice is correct, it might be 3x so double check.).
Bookmaker is the exception with high fees. Some books will transfer for no fee or less of one. Other books known to transfer are 5Dimes and Heritage (pretty sure both transfer with each other and Bookmaker), BetOnline (not sure who they transfer with a lot of books stopped dealing with them), Legends (not sure, they seem to change often too but seems by their own choice).
By fast it is not instant. Even in the old days when there were better bookies for US it would take a few hours. Now is often under 24 hours, but things can get delayed too.
One thing to mention many books will not give a list of who they transfer with. You literally need to run down the list. Do you trade with A, Do you trade with B. It's so silly but that's the way they prefer it.
A final thing to note is 5Dimes has player to player transfers. You can sell, buy and trade 5Dimes cash with friends etc. This needs to be requested via live chat, and sometimes there are delays or they don't send it and need to follow up. But this makes it a decent hub because they transfer with many books and if you know other bettors can exchange for cash.