cubical - 12, maybe 18 months before you'd start to see some degradation. Not saying anything would be rendered useless, but plastic is gas-permeable over time - eventually, air will get in; eventually, your O2 eaters will get full - but most importantly, if you're freezing, eventually you'll want to thaw it out - and then you'll need to control the condensation. This is especially important if you expect to thaw & refreeze & re-thaw a package.
You'd help yourself out if you stuffed those bags in a Mason jar - then you'd only have to worry about the air in the jar, and you don't have to worry about condensation - just let the whole jar come up to room temperature, open on a dry day, get done quickly, and re-pack / re-freeze immediately. (This is being pretty retentive, but the margin of safety is unknown; you may choose to err on the side of caution, and you may not.)
As for the extra $20 - consider what you spent on what you're puttin' up.
Hope some o' this helps