I was trying to buy something off of the deep web. I sent it to the url they gave me, but it still says my balance is still 0. My bitcoin wallet transaction details say "0/offline, has not been successfully broadcast yet".
the answer is in your question
your bitcoins have not gone anywhere..
if you are having problems with your bitcoin wallet.. learn how to get your private keys (which everyone should do to learn how to backup)
and then import the private keys into a different wallet program or service.
the reason your wallet program might show 0 available balance. is because it knows you made a transaction and thus zero's the balance on the display, but behind the scenes it is 'pending' as it seems your wallet program is not connecting to the network to push the transaction.
so by putting your private key into a new wallet program/service, is like a fresh start if your transaction is never going to be pushed by the old wallet program/service. and because the new program/service is not holding the 'pending' it will display your balance as being available, and you can try making the transaction again
also sending funds "to the url" sounds off.. it should be an address, not a url.