How much does it really cost if I buy 1 eurgbp (usd account)?

Hi All,


I have been thinking. If I buy 1 lot eurgbp, then there must be 2 conversions at least if I have an usd account.,..

One from usd to eur and then from eur to gbp?
or one from usd to gbp straight?
How is it done in reality and what prices (middle? ask /bid?)
What will be the cost of this purchase assuming 20 points for eurgbp and 18 for eurusd, and usdgbp 15 ?