Family Dollar has 3 Month XBox Live Gold cards for $10 (down from the usual $24.99). This is the cheapest I have seen anywhere. This is B&M only and not advertised in store. At least it wasn't in the two I went to and none of the people that worked there knew about it.
Turning off recurring billing before redeeming should let you get a free month for turning it back on after redemption but YMMV with that.