I'm sorry but this is ridiculous, and your 'conversions' remind me of the time I tried to use toy money to buy an ice cream as a child.
US Dollars may look more realistic than the pretend money I tried to use back then, but I'm sure you could much more than a mere $1641 for 20 quid. Shit, even the choco coins I sent my nephew and niece for Christmas only cost a fiver between them.
I suppose it all comes down to whether you want something you can play with or sweets. And if I know British kids, they'll take the sweets every time.