1. To avoid spending a large amount of money, as due to some deal or savvy decision. We saved a bundle when we switched service providers last fall. You could stand to save a bundle doing all your Christmas shopping during their Black Friday sale.

2. To cause or allow someone to avoid spending a large amount of money, as due to some deal or savvy decision. In this usage, a noun or pronoun is used between "save" and "a bundle." Being smarter with your house's thermostat could end up saving you a bundle on your monthly energy bills. This multi-use bus pass was a bit more expensive upfront, but it saved me a bundle in the long run!