how much would we save for every 1k by swapping with someone in vegas instead of travel agent?
Depends on what rate each charges really.
At today's rate according to XE.com you'd get $1624.11 for £1000
If you buy online from the post office you'd get $1578 for £1000
So it's about 2.9% or for $1000 and extra free $29
Also the seller benefits to a similar amount so between you you make about $58
Obviously there are cheaper places to buy $$$ from but you get the drift.