126 is 7 times "life" - one for each day of the week.

In Hebrew, each letter also has a numerical value. There's a system called gematria which looks for patterns/similarities in this. So, for example, the word for "life" in Hebrew is composed of two letters whose numerical value is 18. Hence, things like charitable donations, and, in this case, the purchase price of a house are given in multiples of 18 for good luck.