I had assumed it was Roman denarii, or one month's pay, but if they were Tyrian shekels, that 4 months is accurate. Either way, not very much for such a betrayal, especially considering the wealth of those paying for it.

An article on the topic

If we ballpark it at 2 shekels to a modern ounce, that would be 15 ounces, or about $1000. In modern terms, that's less than a month's pay for entry-level work.