Reasons for your consideration:

• The primary current meaning of the tilde is "approximately equal to", which is analogous to the definition of money.
• The squiggly line of the tilde is similar to the vertical or horizontal bar common to currency symbols, but more ethereal to represent a digital transaction.
• The tilde is easily accessible on any keyboard.  I'm writing this on my phone.
• The tilde is easy to draw by hand.