Unfortunately, it's your word against the landlord.
A lawyer can give you a definitive answer. However, the whole idea of a deposit--regardless of size--is to bind you to your commitment. And you sacrifice the deposit if you default. You acknowledge you changed your mind. If there had been a written agreement AND if the agreement had outlined those terms regarding a deposit (nonrefundable if the renter defaults), you'd clearly lose your deposit. Sure, it's possible that the written agreement would have provided for a return of your deposit . . . but there was no written agreement. And you acknowledge, again, that there was nothing either in writing or verbally regarding the disposition of the deposit in case of default.
So, how could you make the argument that you're owed a refund? Well, you could argue that you didn't agree (verbally or in writing) that the deposit was non-refundable. But I can imagine a judge asking, "Well what did you think the deposit was for?" You could try arguing that there was no lease, and therefore that a deposit for a non-existing lease is impossible. But, again, I can see a judge asking, "Well, what was the money for, then, if not a deposit? If it was simply a gift to the landlord, then it was a gift and he gets to keep it."
Sorry. Your position appears very weak. But, then again, I'm not a lawyer and only a lawyer can really straighten this out. However, as a practical matter, you're likely to find that a lawyer is going to cost you more than you might recover even if you were successful.