You simply cannot use an already existing currency symbol for a new currency. Period.
Currency symbol MUST be unique, you can't use existing ฿ unless you want to confuse someone during transaction
Hogwash to both of you. Go tell that to the Mexicans, who don't seem to have much trouble distinguishing their $ (peso) from $ (USD). Or to the Canadians or Australians or Kiwis who use $ for dollar. Or to the Danes, Norwegians, Swedes, Icelanders and Estonians, all of which use(d) "kr" for local variations of "crown". Or the Costa Ricans and Salvadorans, both of whom use ₡ for their currency symbol.
IMHO, introducing a new symbol that's not already in Unicode is a poor idea. It took a year and a half for the (euro currency) symbol to be included in the Unicode standard after the European Commission released the design, and that's the kind of lead time you might look forward to for an "official" government currency.
There are a whole bunch of viable existing "b" codes already in Unicode. Some of them here:
http://www.fileformat.info/info/unicode/char/search.htm?q=B&preview=entity I'm partial to the circle-b/B ones myself.