Value is subjective. But objectively, those collateral items are equivalent to a value of zero. Here's why:

Firstly, Steam accounts can be retrieved easily in a variety of ways after the transfer. Not only that, but I believe it is actually against the rules to sell your Steam account. So, the parties involved would be breaching Steam T&C.

Secondly, BCT accounts can also be retrieved because any password/email changes can be reversed (or the account can be locked) within 14 days. This means that you would have to escrow the account for a full fortnight to get the loan, which would probably be pointless for most people; you would ask for loans when you need them, not 2 weeks in advance.

---

That means... neither of the collateral items are worth anything.