How to bypass a metered connection?

In North America, using Xfinity for reference. I want to create both a home NAS and offline Wiki/media backup. Problem is to get the amount of data I need would blow through my plan and throttle my speed. I guess I could try and do it over a longer period or download just before the billing cycle renews so even if I go over it will reset. I would rather avoid these scenarios, the only other thing I can think of is using a cafe or library connection, that might be what I have to do. Any ideas on places to download massive amounts of data or ways to get around throttling? Thanks in advance.